Instructions
Walk around with Golbat in your party. Every 256 steps you take will raise the Pokemon's happiness level by one.
Take Golbat to the masseuse in Veilstone City for a massage once a day. Each massage will raise its happiness by three.
Feed Golbat rare candies or use him in battles. It will pick up between two and six happiness points for each candy or victory.
Feed Golbat vitamins or EV berries. Each vitamin is worth between two and five points, and each EV Berry is worth two to 10 points. Vitamins can be purchased from the second floor of the Veilstone store. EV berries can be purchased from the Floaroma shop, or found randomly in battles.