Tip #1: Tell your SP that you can only cum once during your time together, and that you would like to make it last. If she's any good, she should be able to bring you back and forth to that almost-there-feeling without making you cum before you're willing to.
Tip #2: Penis-in-vagina is not the end all be all of sex. Try enjoying the ride for the fun that it is, rather than being cum-focused.
Tip #3: Following from Tip @2, in the advent that you do cum early on, nothing prevents you from having more dirty fun between the sheets. You may not cum again, but you sure can still enjoy yourself.
Tip #4: Tease and Denial Baby. Lots of fun.