Feed your Pokemon many rare candies and battle with it. Making them hold a soothe bell and having them first in your party may also help. Make sure to heal your Pokemon before it faints (or it won't like you as much). ~KKMG1
Chat with our AI personalities
the easiest way for me is to give it exp.share and face the elite 4
the easiest way to level up your Pokemon to put it in daycare Pokemon will level up soon.Trade the Pokemon to friend and have it hold a lucky egg it will level up quickly.
Either cheat or "chain" 40 pokemon.
Use items.
The same way you would catch a normal Pokemon. The only difference is is that the Pokemon is shiny.