I agree, use your experience as a sub to help you be a dom. You know what feels good and what doesn't. You know from the submissive point of view what is going through his mind. I am sure at some point you have said that if I was domming me right now I would have done this or that, so now is your chance to act out some of the things you wish your dom would have done.
Above all else, don't think to much, just go with the flow. He will give you signals as to what is pleasurable and what is not. You will be fine.