Instructions
Catch a wild Golbat using a Luxury Ball. Pokemon which live in a Luxury Ball will gain Happiness points twice as quickly as those in normal Pokeballs.
Give Golbat a Soothe Bell to hold -- this item will also double the rate at which it gains Happiness points.
Assign Golbat to your traveling party of Pokemon. Every time you walk 256 steps, each Pokemon in your party will gain Happiness points.
Feed Golbat vitamins like Carbos, Iron, Protein, HP Up, Zinc and Calcium. It will gain some Happiness points for each vitamin it eats. Avoid feeding it Energypowder, Heal Powder, Energy Root or Revival Herb, as all of these will make it lose Happiness.
Take Golbat to Daisy Oak in Pallet Town and get it a massage -- this will boost its Happiness.
Use Golbat in battles so that it gains Experience Points and levels up, but do not allow it to lose a battle and faint. Leveling up boosts a Pokemon's Happiness, but fainting saps it.
Keep boosting Golbat's Happiness points until it reaches 220 and the next time it levels up it will evolve automatically into Crobat.