Decide what style of yodeling you wish to do. There are several styles to choose from--Country and Western, "classic" Country Western, Alpine, Hawaiian, Indian and more.
Listen to examples of each style. For Country and Western styles, listen to Randy Erwin, Janet McBride, Margo Smith and more. For Classic Country and Western, listen to DeZurik Sisters, Elton Britt and other such artists. For Alpine, listen to Franzl Lang, Adi, or the Wild Rose Alpine Club. For the other styles, listen to Annette Hanshaw, Gordon Freitas and more.
Experiment with each style of yodeling, until you find one that suits you best.
Practice until you have the basics of yodeling down, and are proficient. You are unlikely to be able to find a teacher near you, so listen to recordings and keep practicing.
Add your own twist to your yodeling, like the singer Christine Lauterberg, who adds techno to her yodeling.
Compete in yodeling contests. Famous ones are the Germanfest, or the Western Music Festival.