This cheat is how to lv. Up your pokemon at a pretty good rate.

Step I- Trade any pokemon with a friend, it doesn't matter. All traded pokemon gain more experience than "your-own-raised-pokemon".

Step II- if the pokemon you got it weaker than the ones in your party, Do these two things-

A- Put your pokemon in the Day-car until it is the lv. you wish

OR

B-Get an Exp. Point Share and put it on the traded pokemon. To lv. it up EVEN FASTER, go to the Elite Four and battle.

Hope that helped!