Having studied chain woes excessively this summer, including ghost shifting in the back and chain suck in the front...

-check front derrailler clearance over big chain ring. If it's even a mm or two too high, it can throw your chain.

-are chain rings installed correctly? Not off a 1/4 turn, not backwards,

- bent chain ring or front derailleur?

- chain suck, when it actuall gets "sucked" between the frame and the chain rings, and other shifting problems can be caused by shifting under load, operator error

-is the chain worn? Uneven wear between chainrings, cogs and chain can cause all sorts of problems. Replace your chain the very second it starts to show stretching.

for rear derailler problems, check that the hanger isn't bent and that the rollers line up exactly with the largers cog in the back when you are set for the lowest gears... you might have to to take the chain off to check this.

Irulan