shyness self confidence nd my secret desires

I'm a heavy set girl with a imagination and craving for sexual adventure my partner is skinnyer and more in shape than i or ny girl hes ever been with...he wants me to take the lead and make the first move...give him head and get on top and I am intrigued by this nd like the thought but I'm so dam shy and never really he experience I just get nervous il do it wrong really wrong or will screw up somehow and I ALWAYS chicken out....anyone have any ideas tips or tricks to please him HELP ME I want to surprise him with some new move or something !! without completely getting all shy and screwing up