Congratulations! You two are going to have so much fun!

My boyfriend and I are fairly new to all this, too, and it looks like we will never end up being very hardcore with BDSM. Ditto to what everyone said about taking it slow, and great idea in describing really dirty/dangerous fantasies during sex rather than actually acting on them.

A fun way to do that while also learning what she likes would be to tie her up--you could use rope, household items like scarves or belts, or something from a toy shop--and "interrogate" her about her fantasies. Spank her until she confesses, or get her excited but hold back fucking her.

It's always interesting to see people who write, "My S.O. is submissive; I want to learn to be dominant so I can please him/her." Learning to be dominant is also very much about learning to receive pleasure, in fact, to demand it (within the boundaries of your relationship/play). Spend some time thinking about what you would really, truly like her to do to you, without worrying about whether she would enjoy it. For her, her discomfort is part of the fun!

Talk about stuff before and after you do it to make sure it's working for both of you. And be extra sensitive when you're playing--when people are subbing, they can become vulnerable in ways they've never known before, and may need extra cuddling, reasurrance, etc. afterward. You certainly don't want her thinking she really *is* a lousy fuck, especially when she's standing on her head with tassles hanging from her nipples to try to please you.

Good luck!