There are many ways to increase your Pokemon's happiness:
- There is a lady in Castelia city who will give your Pokemon a massage daily
- You can use vitamins (carbos, protein, iron, etc)
- You can use EV reducing berries
- You can also buy stuff from the beauty salon in join avenue
- Certain items from the cafe will also increase happiness
- There is also leveling up but thats not fast. And there is also walking around but its increase is unknown(this also takes a lot of time)
When you do this make sure your riolu is holding the sooth bell because it will increase everything x1.5.