Here are the things I think you should know before going to Iceland.
1. The must-see natural attractions are outside Reykjavik.
To be fair, there are impressive tourist spots in the city such as Hallgrímskirkja and Harpa but the most popular tourist destinations in Iceland are an hour away (and more) from Reykjavik. These are blue lagoon, gullfoss, golden circle, geysir and Jökulsárlón just to name a few.
2. It is convenient and affordable to rent a car in Iceland.
I highly suggest to rent a car in Iceland if you plan to explore. There are several tours in the country but It is expensive for me, at least. If you only plan to travel around the city, it is better to rent a car but if you plan to travel outside the city, rent a SUV. All national driver's licences are accepted, so you do not need to have an international license.
3. December/ Winter is not the ideal month/season to visit Iceland
We were in Iceland last december and I was appalled by the weather during that time. Iceland had a very short daylight and even if the sun is up, it is not very light. Apart from the short daylight, it was windy and raining most of the time. According to the locals I've met, the best months to come to Iceland are March to April and September to October. During these months, Northern Lights can be seen in the city itself. No need to travel to far away places just to see it.
4. ICELAND is the most expensive country that I have been to so far.
It says it all.
5. Strictly follow the parking rules and speed limits.
Driving in a different country is really stressful but somehow educational. In Iceland, there are unrecognizable policemen who walks around the city and checks each car if it was already paid. On the other hand, the different road types have different speed limits and most of the time you will see policemen measuring the speed, and not to be forgotten, speed cameras! :P Are you wondering why I know all of these? Well, we just had a violation for both parking and speed limit. Funny.
The most important thing I learned about Iceland is that they have an extremely bipolar weather, so better be prepared for these swift weather changes. Better rent an SUV because you could just experience snow blizzards from no where. Overall, ICELAND is extraordinarily and naturally BEAUTIFUL!! No wonder why there are countless tourists flocking to this beautiful country!!