I originally wrote the below notes on a 2012 trip to Iceland in late February and early March. I haven’t been back since (though I would love to), so I don’t know how well any of this will hold up. But I present it here in case it is useful for someone. Hopefully I can one day return and maybe then I’ll update! 
Places visited:
Reykjavik
Hofn
Gulfoss
Thingvalur
Geyser
etc.
Places stayed:
Rykjavik hostel
Gerdi (?)
Hotel Orkin
The Reykjavik airport is 30-40 minutes from the downtown city center
If you’re staying in Reykjavik, being near the city center earlier in your trip may be nice (of course this is fairly obvious general travel advice). This way you can explore then, if you return (as you likely will for your departure flight), you’ll probably know generally where you might want to go.
The church in Reykjavik (name) is worth checking out. It has a unique, rather sparse, “Scandinavian” interior, but the lighting is nice, and the church organ is fairly stunning and unique.
Multiple names for things, especially airports? (e.g. Hofn airport) Reykjavik airport is “Keflavic Airport”, rather than e.g. “San Francisco International” or “Denver International”.
Non-English characters can make it hard to type pr spell many place names, especially into GPSs. Try using just the first few letters in a search and scrolling through the options until you find what you’re looking for.
Rent a car. There is decent public transportation in Reykjavik, but going between cities, much less to more remote points of interest, is questionable. The freedom of having a vehicle is fairly incomparable in such a wild, open, and spread-out country.
Law enforcement and speeding.
You’ll want a cell phone. Iceland has good coverage (figure out what networks(s), etc.). Also prepaid, etc.
Your days will almost always be really packed, depending on where you stay, so be prepared for it. From breakfast between 9 and 10 (at the latest), when most hotels and hostels stop serving, to a day of exploration, to evening exploration of local nightlife (mainly if you’re in Reykjavik) or aurora watching, you can be out and active for 12-16 hours. It can be exhausting. Take care of yourself, but you’re probably here for a fairly limited time so make the most of it and push yourself a bit if you can. 6 or 7 hours of sleep may be worth it a couple of nights to get some good aurora watching, for example.
Bring swim trunks for hot springs.
Lots of ponies/horses (you’ll want to call them ponies, but they’re horses); (find out what they’re used for)
Great drinking water (cold), comes from separate source from hot water, highly rated for purity internationally and independently, no additives (e.g. chlorine, fluoride)
Hot water smells of sulfur/eggs, mostly in Reykjavik, but won’t stick to you. Comes from hot springs. Avoid drinking it.
Weather can change at a moment’s notice, don’t give up if it sucks in the morning or afternoon, go out, see stuff, hope and expect that it will change in your favor.
Seeing stuff covered in snow has its charm, a stark, rugged beauty, but mostly things look better without the snow, especially for photography where the snow makes for flat lighting and many features covered up. A good example are the various waterfalls where their outflow may be completely invisible.
Aurora photo basics in less than 20 words: take a good camera and tripod, shoot manual, f/2-4, 10 -15 seconds, ISO 800-1600, focus manually to infinity.
Use a remote trigger for your camera, if possible (to avoid camera shake from pressing the shutter release). If you don’t have a remote shutter release, try to buy one (they’re fairly inexpensive for basic ones) before you go, or use a short ~2 second timer so that you have time to remove your hand and let vibrations dampen before the shot is taken.
Aurora sometimes move quickly and exposures longer than 15 seconds will tend to blur the details, but for any compact camera, and even many normal dSLRs, you may have to go for longer exposures or accept more noise due to high ISO. A full frame dSLR is ideal for low noise and high light gathering.
After your aurora shooting is over, don’t forget to reset your camera settings to something more “normal”, i.e. ISO 100, f/2.8, 1/250 shutter speed, (or back to Aperture/Shutter priority), and turn off any timer you may have enabled. This way when you take your first shot the next day, it will probably work rather than being a blown-out mess. I’ve missed quick-shot opportunities in the morning after a night of aurora photography because of this.
If you’re a photographer, be sure to take time to enjoy everything with your eyeballs! It’s all too easy to get caught up in getting the “perfect” shot, figuring out the right settings, framing the scene, etc, etc. when nothing you do in the camera will ever beat – or even likely equal – what you can see with your eyes.
There are never enough outlets. Get a travel mini power strip. Recommendation:
Bring outlet adapters for your country, be sure they’re circular-shaped so they fit properly all the way into the outlets. Recommendation:
Hostels are not necessarily a good deal. Compare prices with hotels and evaluate the amenities. In particular, consider food prices as food is expensive and so can raise the cost of your stay each day buy $15 or so per person. Some hotels have breakfast included, as well as other amenities.
Wireless Internet is, as a general rule, pretty poor and unreliable (at least in my experience, staying at 3 different places, plus intermittent use at other locations). Wireless routers frequently needed resetting and staff was not necessarily on top of doing so (though are generally happy to do it if you ask nicely, and often aware of the general flakiness).
Food is comparatively expensive, especially if you’re from the US or any country where eating is cheaper than the US (which is many/most). Food preparation/quality is also not excellent. When you pay for quality, portion sizes are usually on the small side. Expect to spend no less than $10 for a burger and fries, and that’s at a fast food place; at any normal sit-down restaurant a burger is probably near $15, and at an even slightly upscale place the burgers can be $20 or more yet are not more high quality or enjoyable than the $10-15 ones at cheaper places. Nonetheless burgers are plentiful and often the cheapest item on any restaurant’s menu, meaning you may end up eating a lot of mediocre burgers if you’re cost-conscious. More expensive standard entrees average $30-40, and go up to $50 or $60 at even moderately upscale restaurants. Some deals can be found for e.g. 3 course tasting menus for $50-60, and these should be enjoyed when possible.
The fish and chips place in Reykjavik is absolutely worth it. It’s quite popular though so keep that in mind.
Being a vegetarian in Iceland is not too difficult, but your options will be pretty limited.
Being gluten intolerant in Iceland will be harder as many meals, especially breakfast, are based largely around bread and other things with gluten. Rarely do you see gluten-free items noted on menus, etc. though there are some.
Duty free is apparently a good deal, at least if you already planned to do some shopping during your stay.
Tax free thing?
Gas stations, pre-pay is setting maximum, not actually paying; if you pump less, you pay less (confirm?). Gas stations as a general rule want you to use a card with a pin (e.g. a debit card in the US), non-pin credit cards won’t work because it always asks for a pin.
Most credit cards in Iceland (and much of Europe) have an RFID chip in them making wireless transactions possible. Most card readers have the option to also swipe your card, but occasionally you’ll find some that don’t. Be prepared for this.
Tax, etc. is almost always included in prices.
Tipping is not an expectation, in general. Tip jars are mostly due to tourists, especially from the US. Tipping is nice if you really liked the service, but don’t worry too much about it, and certainly don’t aim for the e.g. 20% for “good” service that is typical in the US. The people serving you aren’t being paid below living wage and expected to make it up in tips, and the high prices of food can be partly accounted for by the living wage paid to employees (plus VAT).
Ice cave tours are totally worth it. Try icetours.is (?)
If you’re trying to take a picture of sunrise/sunset on the ice fields at the mouth of the glacial lagoon, in the winter time you’re more likely to get direct light from sunrise. Sunset can create nice reflections if the sky gets colorful though.
Ice is best viewed shortly after moderate rain as it washes it clean of snow and dirt. This is also true for ice caves, where snow above the cave can limit the amount of light that filters down through the ice to illuminate the cave. If you get lucky you’ll be able to go on a tour after it rains and before it snows again.
Rental cars will often have something wrong with them, not necessarily something huge, but it’s a tough country on vehicles.
The Blue Lagoon is sort of on the way from the airport to the main city of Reykjavik and nothing else is really out that way, so if you’re not in a hurry and you have a car (that you can leave your luggage in), consider stopping there on the way to where you’re staying. This is especially good if you get in early-ish and have several hours before check-in time. You can soak in the lagoon, relax and de-stress while you wait, maybe even grab a bite to eat (I didn’t try the food, but after seeing prices in town, it’s not that unreasonable).
The Blue Lagoon is expensive, more so than you might think for not even getting spa treatments (which are available but cost even more), but it’s worth it. You will probably want a drink so don’t be tempted by the lowest-priced option, just go for the Comfort package with the included drink, towel, and robe (unless you have your own towel, in which case… maybe not?).
Swimming shorts are available for rent if need be, but of course you should have brought your own to Iceland!
There is a hot waterfall at the building-side of the lagoon, great for washing off mud.
Next to the waterfall are a dry sauna and wet steam room, both should be free for use.
Drinks at the Blue Lagoon are decent, try the green one with ginger if available. It’s a novel experience to float around drink in hand.
There are mud pots at the wooden boxes around the edges of the lagoon. They’re full of special mud that’s supposedly good for the skin. You’ll probably see people over near them smearing mud on or letting it dry on their faces. Give it a try, it’s novel. You may also see staff wandering around the pool with additional skin treatments to try (generally for free). Whatever you do don’t cover yourself in the mud you find on the bottom, in fact, don’t bother doing anything with it but squishing it between your toes, it’s best left uninvestigated.
Go to the lake near Gulfoss, down a side road, and you might find amazing wind-blown ice on the shore. More generally, try to figure out the overall direction of wind on partially frozen lakes and look for similar ice pilings on the downwind side.
Avoid aurora tours, the crowds make things much less enjoyable and peaceful, and often they’re full of amateur photographers using flash and other annoying things.
Scout your aurora viewing locations during the day, if at all possible. Locals may give you good advice on likely viewing spots, but finding isolated spots off the beaten path is really ideal.
If photography is your thing you’ll want to find good foregrounds and backdrops for your aurora shots. Scouting is doubly important here because while there are generally good areas, the specific conditions can dramatically affect how good a particular location will look in photographs, e.g. whether there is ice piled up on the edge of a lake or not, whether there is snow on a mountain or not (if not, it will tend to be just a dark mass, but perhaps a silhouette is what you’re aiming for), etc.
Driving from place to place may take longer than you think, especially when snow, rain, or other non-ideal weather are a factor.
Turn off your brights as soon as you see another car, they’re touchy about it.
There are 1-lane bridges, especially on the southern part of the Ring Road (Hwy 1?). You’ll see signs to indicate the narrowing road, approach with caution, if you see another car try to ascertain whether it is on the bridge or will enter it before you; if so, stop before the road narrows to a single lane. Don’t be afraid to back up if you go too far but think the other car has the right of way.
Get an offline navigation app. There’s a free one on Android called “Navigation” from (who?). Its interface is a bit quirky but it’s generally very functional, useful, and accurate. It compared well to a car-mounted Garmin GPS on my trip. Use the OpenStreetMaps option for free.
Recommendations:
Accomodations, Hotel Orkin, free breakfast, tea+cake free all day/night
Noodle House, cheap, filling, decent.
You will probably wish the speed limit were higher. It’s easy to speed. It makes a lot more sense when the weather is anything but perfect.
Old Notes (from Keep)
4wd not overkill
There are speed cameras. GPS can help identify. Also signs?
Rotten shark is an interesting stop, but it costs 800 kroner per person.
Persistent header, I don’t claim to be authoritative or comprehensive. It’s just one person’s perspective from a given trip.
Having a gps is pretty necessary. Having 2 to check each other is even better. One can be your phone with offline nav.
Bring a car power splitter.
Bring a phone car charger.
Gas prices are remarkably similar so don’t worry about it. But many are unmanned.
No window washing stations at gas pumps.
There is a Reykjavik airport, so the airport name thing is probably not helpful. But distance is still important.
Mention car rental company?
You probably won’t hear as much sigur ros as you expect.