Summarize:

Once the deed is done, get comfy and plan to stay a while. There is a certain level of respect that should go along with sex, and unless she indicates otherwise, it would be inconsiderate to sneak out or make excuses for why you have to leave. Relax and take pleasure in each other's company for the night, then go your separate ways when the sun rises. Leaving immediately after you're finished sends the message that you don't even want to be around her, which can easily ruin the experience for her. Remember, you're with another human being, and they have feelings that can be hurt. Resist the pressure to do a lot of cuddling or kissing after sex, and don't start telling her how much you like her. There may be an expectation to bring emotions into the mix. However, this will only complicate things for both of you. Be nice and act friendly towards her, but don't make promises you don't intend to keep. If you've been honest about what you're after, there should be no reason to make your time together seem like anything more than what it is. Never say "I'll call/text" you if you have no plan to. The two of you should be clear on what level of communication is appropriate before you part ways. It may be that you're both content with the fun you've had and don't feel the need to see or talk to each other again. Or, you might like the idea of becoming casual friends and sending each other a text once in awhile. Restate the fact that you both agreed it should be a one-time thing. Keep things light. You don't have to send each other a friend request on Facebook or schedule another time to get together just because you kept each other company for a night. Sometimes feelings can develop unexpectedly. If that's not what you want, say so. Remind her of your original arrangement. Be firm (but not rude) if you have to. Rather than walking off with your clothes in your hand and your head hung in shame, be appreciative of the time you shared. Thank her for showing you a good time and let her know that you enjoyed getting to know her a little. Sex should be a pleasurable interaction with no regrets. There's no point in having a one night stand if it leaves you feeling disgraced. Reassure her that you'll be discreet about the details of your encounter. If you do things the right way, having a one night stand can exhilarate and satisfy both individuals without causing any awkward fallout.
Spend the night together. Don't send mixed signals. Make it known that further communication is optional. End on a high note.