i don't mind carrying passengers at all as long as they know how to ride, and if not, they must follow some simple rules that i have which "generally" teaches them the "rules" of being a passenger.
#1) when entering AND exiting corners, lean with the bike and DON'T SHIFT YOUR BODY.
#2) when riding, pay attention to the road with me so you will be prepared to enter corners, maneuver around obstructions, etc... and DON'T SHIFT YOUR BODY.
#3) if you are feeling uncomfortable, DON'T SHIFT YOUR BODY. tell me and wait until i tell you its ok to move.
#4) if the passenger is a female, they are required to hold onto me at all times with both arms wrapped around me (this one is pretty self explanatory
basically, using the simple rule of DON'T SHIFT YOUR BODY will significantly reduce the amount of movement from the passenger which will allow you to concentrate more on the road and conditions rather than concentrating on compensating for a moving body behind you.
its very stressful when you are fully into a corner and your 120 pound female passenger decides to push herself up off the seat to adjust her butt position.
make sure the passenger is comfortable and ready for you to move PRIOR to putting your bike into gear. this will help prevent them from being tempted to shifting their body.
in short, one rule. DON'T SHIFT YOUR BODY. after that, everything else is all easier to deal with on an individual learning basis.