Answer:
1. Take loads of drugs in order to go completely insane
2. Face years of rejection and sadness in order to find it arousing to hurt people
3. Listen to death metal nonstop
4. Buy loads of latex and leather lingerie
5. Write a CV detailing on steps 1-4 and send to a reknowned S&M whoreshack
This answer is horrible, and completely wrong.
So, the real answer is Find you local dungeon and speak with someone there to see if this is really for you.
Find a Dominatrix who is well known and respected in the community and ask to be mentored.
Don't do anything until you've had proper training. YOU COULD KILL SOMEONE doing this stuff.
Good Luck and Happy Beatings.