Be Prepared for Human Breakdowns
People, believe it or not, are machines, too. At least, that's how you should think of yourself while adventure cycling. You require fuel, downtime for repairs (rest), and protection from harsh operating conditions and contaminants.
Almost inevitably you or someone in your group will "breakdown" at some point, on some trip. Whether it's one of you running completely out of energy (known in the cycling world as "bonking"), or getting hurt in a tumble from the bike, physical challenges are simply a part of cycling. The best defense is to guard against them by carrying a first aid kit, taking frequent opportunities to eat and drink and knowing who to call if someone needs immediate, professional medical attention.
Now brace yourself: Here's where you need to take care of some dull, administrative stuff. Long before you hit the road, find out what your insurance will or won't do for you if you need medical treatment while cycling, especially if your trip is in a different country. Will you need an extra rider (no pun intended) on your traveler's insurance? Will you need immunizations or special medicines, like anti-malaria pills, while you're there? Do you expect the water to be safe for drinking? These are all things you definitely don't want to learn by surprise.
Another one of those near-inevitabilities: one person will be slower than another if there's more than one of you. This can prove highly frustrating to the slower person and downright annoying to the faster one(s). Everyone just breathe and relax. Remember that it isn't a race. You're there to enjoy the scenery, the camaraderie and the journey.
Finally, know the limits of your own skills and equipment. Just because you saw a rider hammer that suicidal downhill like she was a mountain goat doesn't mean that you can do it, too. In adventure cycling, discretion is often (usually) the better part of injury avoidance.