- Book the ferry well in advance. As soon as possible, basically. I booked my ferry 6 (!) months before I was to actually leave, and already some spaces were sold out. The sooner you book, the better. Meals can be booked in advance too, but that's not really necessary.
- Fit new tires, inner tubes & wheel bearings before departure. I had fresh Heidenau K60's when I got to Iceland, and the rough tarmac just ate them up. Especially if you plan to go off road, new rubber will pay off in spades. Also a new chain set will be valuable, with all the dust.
- Make sure your sleeping bag works at freezing temperatures, by actually testing it in the cold. My sleeping bag says it works at -2.5 Celcius, but time and time again I was woken up at night just because of the sheer cold. Regardless how warm it is during daytime, the night will always catch you off guard if you haven't brought the right gear.
- Bring your own ratchet straps. Dear God, I can't stress this enough. Deckhands do not help you strapping the bike down, and the straps they have on board are highly insufficient. You can get a good strap at any hardware store (the ones with proper steel hooks are perfect), so just test it before you depart, and you'll be golden.
- Bring a rain coat which fits over your normal motorcycle coat. This isn't so much for the rain as it is for the wind.
Once you're there:
- Routinely check your bike for undone bolts. The rough going in Iceland will shake stuff loose - better catch it sooner rather than later.
- Do not venture off onto the F-roads alone. You can go on for miles and miles without seeing another soul, so if you're stricken for help, you're done for.
- Fill up when you can. There's easily a 100 km between pumps, and you don't want to miss a particular sight because you gunned it past the last fuel stop. Routinely check your map for available filling stations.
- Know your bike's mileage fully loaded. Most petrol pumps work on 'pay before you fill up' basis, meaning that you have to give the amount of ISK you want to spend before filling up. So if you know how many litres you need, you know how much money to spend.
- Beware of the wind. It's a constant in Iceland, and yet sudden gusts will be able to send you off the road easily (like they did to me)
- Watch the sheep. Sometimes they'll gladly sit in the middle of the road with you coming at them with 90 kph, scaring the crap out of you. Never pass them at speed if they sit in or near the road, as they might get startled and run in front of your bike.
- Keep an eye on the weather forecast, if possible. You don't want to get stuck in a certain area because of the weather!
If you have any further questions, feel free to let me know.