Look up kegel exercises and DO THEM. They help enormously.
Look up techniques for giving her clitoral, g-spot, deep spot orgasms and practice them on her. If you give her at least one before penetration, the pressure is off you to "perform" and you can relax. The foreplay from kissing, taking clothes off, and giving her an orgasm first, should be AT LEAST 30 minutes to an HOUR.
When you start, start off really slowly. Like, really shallow, really really really slow strokes, whilst you caress her and kiss her. You can build up incredible amounts of anticipation, and with the right dirty talk where you tell her how beautiful she is to you, and then ask her how much she wants you to fuck her, and so forth, you can build it up until she's BEGGING to be fucked by you. Then, if you just start nice and slow you can build up your pace. Try and visualise your arousal level, where 0 is totally flaccid, and 10 is you're ejaculating. You want to start off nice and slow around 5 and 6, so you're hard and experiencing some sensation, but in no danger of blowing. You want to focus on maintaining about a 7, whatever pace and depth that requires. If you start feeling like you're veering towards 8 or 9, just slow down or even stop, kiss her a bit, and then continue. Positions in which your body has the minimum amount of tension are the best, because you can relax your muscles (especially your PC muscle) and are less likely to go too far. Deep breathing also helps relax everything. A simple set of positions would be
Missionary to start - you can control the really slow initial thrusting, and with good eye contact you can kiss her neck, whisper in her ear, and build anticipation. Dirty talk at this point would be along the lines of how sexy she is, how you can't wait to be inside her, how does she like your hard cock in her tight little pussy, how badly does she want to be fucked by you, etc.
Her on top - this one, you're completely relaxed and she's doing a lot of the work. She can set a pace and if it gets to much, you can just pull out or grab her shoulders and neck, pull her towards you, and tell her your gonna fuck her HARDER (what you actually do is SLOW DOWN the pace but thrust a bit harder, meaning you can get back down to that 7 mark, but engage her mind and make her believe it's getting MORE intense). Dirty talk at this stage is more aggressive, how she's a naughty girl tell her to ride your cock harder, slap her ass a bit, etc.
Doggy to finish - women LOVE doggy for all kinds of reasons. The main one is that, with you coming from an angle above her, it can stimulate either the g-spot or the deep spot almost perfectly. Coupled with more aggressive dirty talk (how she loves to get fucked like an animal, how she's your dirty little bitch, how she wants to cum like a fucking slut all over your hard cock, etc.), slapping her ass, pulling her hair, it's a very dominant position, which most women enjoy, and it's a good one to get her to have a vaginal orgasm whilst you're inside her.
If you last about 5-10 minutes in each position, that's 30 minutes of penetration before you cum, and she's definitely gotten one before and hopefully one more to finish, and you've gotten a good hour to 1:30 of total sexytime in there.
*NOTE* Why did I emphasise dirty talk so much? Because it's REALLY FUCKING IMPORTANT. The female orgasm is almost entirely mental. The mechanics help her get there, but the wrong mentality can totally block it, and the right mentality coupled with the right words and get her there more quickly, more easily, and multiply her sensation by 10 or even 100 times.
At the beginning, telling her how sexy she is TO YOU is really important because women love to know that they're wanted and desired by you. It turns them on to know that you are turned on by THEM.
As you start, you can use leading language to heighten the experience for her. The sexual state is a trance state, and thus hypnotic language patterns, suggestive language, etc. will work to create images in her mind, and sensations in her body. If you tell her "every time I touch your body you feel more and more aroused" she WILL become more aroused as you touch her, just by the virtue of having said it.
When she's having an orgasm, being able to read the signs that it's coming, building the anticipation, and then TELLING HER to cum for you, is immensely powerful, especially if you tell her to cum as hard as she can for you like a good girl. This also anchors your words to her pleasure and builds massive amounts of trust in you and what you say - to the point where you can even tell her to cum on command without even touching her!