I know it's just a myth, but it's really become a good luck charm by now. When I play the older games, sans touch screen, I press and hold B so hard that I sometimes damage the button. On newer games, I press my stylus right to the middle of the button of the Pokeball shape on the touch screen.
I also rock my system back and forth in time with the ball.
it depends on ball
for normal pokeball i just keep tapping a
greatbal i do a but only every two
ultraball a+b tapping
safariball b tapping and the rest mostly a+b or l+R
i only do nothing at masterball
It depends on the game, but the idea is generally the same. I draw the path of the Poke Ball(or just point the d-pad in the direction it's flying, hold B when the Poke Ball opens, press A once it's closed, and then draw the shaking(or move the d-pad with it) until it's caught. I've never actually noticed a difference between when I do that and when I don't, though. Hmm...
Years and years ago my cousin tried making me believe that you could do more damage in Pokemon Stadium by holding some ridiculous button combo. In the Project 64 emulator you can put a cheat on so if you hold 'L' it OHKO's your opponent XD so I guess there is a combo to do it.
Up and B all the way! Although as a kid my friend told me that when I threw a pokeball (I am using a gameboy advance SP BTW) that I should mute the system, close it, and toss it in the air and I would catch. It actually ended up working sometimes.