Instructions
Catch the Pokemon with a Luxury Ball or Friend Ball. A Luxury Ball doubles the happiness gains when any of the events which raise Pokemon happiness occur. The Friend Ball only appears in second generation Pokemon games and remakes, and sets base happiness to 200 when the Pokemon is caught.
Walk around with your Pokemon. Your Pokemon's happiness is raised by one point for every 256 steps you take.
Level up your Pokemon. Your Pokemon gains 2 to 5 happiness each time it reaches a new level.
Groom or massage your Pokemon. In every version of the Pokemon games, there is a character who will groom or massage your Pokemon once a day.