Well, I agree with the rubbing of the clit for sure. Try rubbing it while he is doing you vaginally and think about anal then he can slowly start slipping it in, that works for me. Also You might consider a condom it helps it be more slippery. TIP#1:If you are rubbing your clit and you feel like your going to get off before him slow down, chances are once you get off you may not be able to continue. TIP#2: You may want to clean out a couple of hours ahead of time to ensure no messiness. TIP#3: Wet makes a lube that is thin, it works great (the thicker the lube the more the friction).
Good luck
Abbey