How do I tune a front derailer?

Start with the H and L screws. The L screw stops the chain dropping off the small ring near the frame. If the chain falls off toward the frame, screw the L screw in. If the chain rubs on the derailure nearest the frame, the screw the L screw out. The H screw stops the chain falling off the biggest cog away from the frame (toward the pedal). If the chain falls off the big ring towards the pedal, screw the H screw in. If the chain rubs on the derailure on the side away from the frame (nearer the pedal, screw the H screw out. You can also adjust cable tension with the adjuster near the gear shifter.