Right of Way
The rules for kiteboarding are mainly based on sailing and windsurfing.
Coming from windsurfing, the term "starboard tack" is quite well-known around the world. This is the same as "right hand in front".
It means, if you are riding and someone rides towards you, with the exact upwind course as yours, someone has to give the right-of-way (RoW). In this case, the starboard or right-hand-in-front rule gets used by the majority of the kitesurfers worldwide.
If you are riding towards someone, and you have your right hand in front on your bar, you have the RoW. The rider coming towards you, then has his right hand at the back part of his bar, and his left hand in front.
The rider with the left hand in front, should give the RoW to the rider with the right hand in front.
Practically, the rider with the right hand in front, should fly his kite further up and stay on his course. The rider with the left hand in front, should ride downwind and fly his kite low, so both kites and riders can pass without any problems.
Now if a rider is more upwind of you, and even if you have the right hand in front, you should lower your kite, and let the other rider keep riding on his course, since you will not make as much upwind to be facing him, and you shouldn't even try. Meanwhile the other rider should fly his kite further up to avoid any collisions.
Use your common sense to judge the situation correctly. Don't insist on your RoW, even if you know the other rider is more upwind than you. Understand that beginners have no ideas of the rules; so once you ride towards someone analyze their skills quickly and judge accordingly. You can also give signals that you will insist on your RoW. Sometimes the other rider cannot change course due to other riders or hazards; this extended situation should be anticipated and then act accordingly.
To avoid collisions, anticipate, and do a turn before problems may arise or just stop in the water with your kite high up and wait until a dangerous situation gets solved.
Never do a sudden change of course directly before the other, this can lead to very bad accidents.