1. Research www.mana.org is a good place to start because Mana supports all kinds of midwifery practices and has good definitions of each.
2. Decide where you want to practice (home or hospital)
3. Take into account the laws of your state or country
4. Choose an appropriate program that fits your lifestyle
I'd say the first step is to read, read, read, and maybe read some more. Talk to people in the birth field - midwives, doulas, etc. See if you can attend some births as labor support. Then (or concurrently) follow Allison's excellent advice!