Some tips I can provide for increasing the Happiness faster are.
- Equip it with Soothe Bell. This increases the happiness they receive for battling.
- Give it Vitamins and Berries*
- Just having the pokemon on your team can also increase it's happiness so make sure and do that.
- If you are playing one of the 4th Gen games you can view it's happiness by using one of the Poketech apps.
- Give the pokemon massages. You can find massages at Veilstone City or Ribbon Syndacite.
*Berries:
Pomeg Berry raises happiness but lowers Hp Ev's
Kelpsy berry raises happiness but lowers Attack Ev's
Qualot Berry raises happiness but lowers Defense Ev's
Hondew Berry raises happiness but lowers Special Attack Ev's
Grepa Berry raises happiness but lowers Special Defense Ev's
Tomato Berry raises happiness but lowers Speed Ev's
Here's somethings to Avoid so your pokemon's happiness doesn't decrease.
- You should never feed it anything bitter.
- Try to keep you Pokemon from fainting.