In Black 2, you can raise your Pokémon's happiness by doing the following:
* amount differs based on your friendship level — 0-99, 100-199, and 200-255, respectively
** amount differs based on your friendship level — 0-199, and 200-255, respectively
† 6% chance, 20% chance, or 74% chance, respectively
- Getting a Beauty Cut at the Beauty Salon (+40)
- Getting a Smile Cut at the Beauty Salon (+30)
- Getting a Shampoo at the Beauty Salon (+20)
- Getting a Massage at the Medal Office (+30, +10 or +5)†
- Getting a Friendly Combo at the Café (+20)
- Getting a Friendly Lunch at the Café (+10)
- Getting a Friendly Drink at the Café (+5)
- Using friendship-raising Berries (+10, +5 or +2)*
- Level up in battle (+5, +4 or +3)*
- Battle against Gym Leader/E4/Champion (+5, +4 or +3)*
- Using a vitamin (+5, +4 or +3)*
- Using a wing (+3, +2 or +1)*
- Walking 128 steps (+2 or +1)**
- Learning a TM/HM (+1 or +0)**
- Using a Battle Item (+1 or +0)
Source