Think about how you want your day-to-day life as a dominant and submissive to go. Does he bring you coffee on a tray naked? Do you require him to be naked? Does he get to sit on the couch?
If you have the small ducks in a row, then the big ones will keep track of themselves. If you know what you want, then the submissive is a lot more relaxed because there is a framework for them to work with. The framework (rules and regulations) can be an evolving thing, but there should be something there to begin with. I would think it would be very hard to go from a straight vanilla relationship into a BDSM one.
Also, scening. With my dom and my sweetie both, we started off mild and built up from there over the course of many scenes. There were times when I just really wanted my sweetie to whale away on my butt, but he was brand new to his sadism and went slowly until he saw how I reacted, and what he was comfortable doing.
So, know what you want, at least in general terms, and how that is going to translate into a relationship, and take the pain stuff slow until the two of you are in sync with what you enjoy. Easy! ..... and fun, so don't stress too much. This is supposed to bring you joy