A basic list: If you like, then it's your like. If you'd do it if you had to - it's a punishment if you would never ever do it, then it's a limit. Start by thinking about the following:
Would you like to dominate, submit or both?
Anal
Bondage
Clit torture
Degradation
Forced orgasms
Humiliation
Nipple pain
Orgasm denial
Pictures
Pussy pain.
Spanking