Since it evolves with high friendship, do things such as:
- give it a Soothe Bell
- feed it EV reducing berries or vitamins
- level it up
- give it massages/ grooming
- feed it meals at Join Avenue
Just walking around with it will also help, so maybe give it an Exp. Share and fight with a more experienced Pokemon in its place. I don't know which generation this is and what you have to work with, so that's all the info I can give.