What is an easy way to level up Pokemon?
To level up a Pokemon quickly, go to Victory Road. In slot one of your party, put a strong Pokemon (level 55+ minimum). In any other slot, put the Pokemon you want to level up, holding the Exp. Share. Battle the wild Pokemon and trainers in Victory Road to level up your Pokemon.
NOTE: Do NOT use Rare Candies. Although th elevel up your Pokemon, they do not raise the attack, sp. attack, defence, etc. of that Pokemon. Also, do NOT leave your Pokemon at the daycare center. They will delete a random move when your Pokemon is trying to learn a new one. The Pokemon's happiness will drop, making it harder to evolve some Pokemon if maxed happiness is needed for evolution (such as Golbat --> Crobat)