Poke ball

No, I'm afraid there isn't a button sequence that will help increase the chance of catching a Pokemon. If you are trying to catch Legendary Pokemon then sometimes these take a lot more than 20 Ultra Balls to catch it, and sometimes it may only take a few, so just do what you're doing currently and you should eventually catch the Pokemon you're after.

Hope this helps,
~Geezerguy

Your game MAY be glithed. But there is an alternative method to catching higher level Pokemon without even knocking a single hp from it's bar. You will need:
A.) around 20 great balls (or ultra etc great balls work fine/are cheaper)
B.) 5 revives (in case Butterfree gets ko'd)
C.) 10+ super potions
D.) 5 either's (in case PP drains out)
E.) Butterfree (at least Lvl 20 but the higher the more successful)
D.) Strong backup pokemon

Save the game! Now put Butterfree first in your pack and then find the wild Pokemon you want. Use "Sleep Powder" right off regardless of opponents level and start throwing the balls. If it wakes up and damages Butterfree use potions and continue process "Sleep & throw" if Butterfree gets KO'd send out backup... And use it's turns to revive, heal and restore Butterfree's PP and then send it out again. Unless your game is truly fried you should have no problem. I used my Lvl 62 Butterfree to capture Lvl 50-55 Kadabr, Magneton etc(Cerulean Cave)FLAWLESSLY without knocking a single HP from the opponent. Butterfree has also allowed me to capture the 3 legendary birds (obviously had to weaken them but), and Mewtwo without using the dam masterball! If you still have the issue either start a new game or Trade it in at Gamestop for another one.

Well I guess caught a Legendary Pokemon is very hard but not impossible.For example I already caucht all the tree legendary birds(Zptos,Articuno and Moltres),Moltres I caught with a Great Ball and Zaptos wiyh a normal Pokemball!Anyway the best trick to caught then is put the for sleep our take down their HP

None. If you're struggling in that situation, attack it using uuuummmm... Leer, Scary face, Growl, Sand attack, or anything that will make their attack, defense, accuracy, etc decrease.