In-game reset
While playing a game, press Select + Start + A + B.

Suspend game
While playing a game, press Select + R to suspend the game without turning it off. Press Select + L to resume.

Screen Off
When playing any gameboy adv.game that can only be played on gameboy adv.push r and select at the same time to turn off the screen (try a few times to get it, it most likely won't turn the screen off the first time.) Than to turn the screen back on push L & select (the screen will probly turn on the first try.) The game pauses and leaves the GBA on. This trick will save power on your GBA.