Instructions
Catch your Pokemon in a Luxury Ball. Pokemon that live in Luxury Balls gain Happiness at double the normal rate.
Give your Pokemon a Soothe Bell item to hold. This will double the amount of Happiness Points the Pokemon will earn from any event.
Add the Pokemon you want to build a friendship with to your traveling party. Every time you walk 256 steps with a Pokemon in your party, it will gain one Happiness Point.
Feed your Pokemon vitamins such as HP Up, Carbos, Iron, Protein, Calcium and Zinc. If your Pokemon's Happiness is under 100, it will gain five points. If it is between 100 and 200, it will gain three points, and if it is over 200 then it will gain two points for every vitamin you feed it.
Take your Pokemon to get a massage from the Massage Lady in Veilstone City. Her house is the one nearest the gym on the south side of the city. Getting a massage will increase the base Happiness of your Pokemon.
Use your Pokemon in battle so it gains Experience Points and gains new levels. Each time a Pokemon levels up, it gains some Happiness Points. Don't allow your Pokemon to faint in a battle though, as it will lose Happiness Points every time it is knocked out.
Avoid feeding your Pokemon Energypowder, Heal Powder, Energy Root or Revival Herb, as all of these cause your Pokemon to lose Happiness Points.