Go to Seven island and go to Sevault canyon and battle the rangers in that area. They make your Pokemon level up faster since their Pokemon are level 50's! But you should have an exp share so example if your trying to evolve your Phanpy into Donphan. You can't battle your Phanpy against those level 50 Pokemon since Phanpy evolves into Donphan at level 22. And some helpful advice; the exp share is found in the building where the guard sits east of Fushia city. Go in that building and go up the stairs in the building. There will be a man that looks like a scientist up there. If you have 50 or more Pokemon in your Pokedex he will give you the exp share.