cheat
In my opinion, I always goto the elite four (aftergame) and replay them. You can also goto the east side of Unova and fight wild pokemon.
Mii Channel
you should give it a lucky egg and put it at the front of your party while you face the elete 4
try rare candies
Pokemon day care or put exp.share on a weak Pokemon
To get a Pokemon level up quickly is to have a Pokemon hold exp. Share and then just battle a bunch of trainers or wild Pokemon.
By battling Pokemon that you are comfortable with and winning them, but there is a choice, battling Pokemon that you are strong to, continuously. Or battle Pokemon you are weak to but can still kill them.
keep battling Pokemon and people
either cheat or battle the as many trainers as possible
Defeating Pokemon that are a higher level that it, or Rare Candies.
Dark Cry? There is no such game. I belive you mean how to level up the Pokemon DARKRAI. Correct?
If you have the Exp.share give it to your Pokemon that you want to level up then go to beat the elite four and the campion