Masturbating before you get together with your partner should help you last longer than usual. Condoms and kegel exercises (google it), are likely to help you last longer, as well.
If you masturbate too much (a different amount for every person), you'll desensitize yourself, and have trouble coming, or not be able to come at all, with a partner. If you find yourself in that situation, the solution is to cut way back, or stop masturbating altogether, until sensitivity returns.
If you're looking to last longer then it not so much whether you do it more or less but rather how you do it.
Taking it slowly and to almost the point of ejaculation then stop for a minute or so and start it up again doing the same thing as you reach the point of just before "no return".
Using this technique and the Kegel exercises mentioned before, and hour or longer used to be the norm. The problem arises when you get married and she turns out to be one of those, "get up-get on-get off" women.