1. Begin sexual activity as usual, including stimulation of the penis, until you feel almost ready to ejaculate.
2. Have your partner squeeze the end of your penis, at the point where the head joins the shaft, and maintain the squeeze for several seconds, until the urge to ejaculate passes.
3. After the squeeze is released, wait for about 30 seconds, and then go back to foreplay. You may notice that squeezing the penis causes it to become less erect, but when sexual stimulation is resumed, it soon regains full erection.
4. If you again feel you're about to ejaculate, have your partner repeat the squeeze process.
Repeat this as many times as necessary, because you will reach the point of entering your partner without ejaculating. Remember practice makes perfect and after a few practice sessions, the feeling of knowing how to delay ejaculation will become a habit that no longer requires the squeeze technique.
Another possibility to prolong your performance is practicing while you are masturbating. When you feel the need to come then stop what you're doing. Also there are ways to control it while you are doing it yourself, by contracting your pelvic floor muscles. You will know which muscles they are if you try to stop yourself when you go to the toilet to pee. If you increase the number of times you contract and release them during the day (and you can do it while you are at work!) :) then you can control your orgasm too.
And lastly stop thinking about it, and how your performance is, because, as surprising as it sounds, women don't take note of these things, if they are satisfied, and you are a generous, considerate lover, then they won't notice how long you are in them. Trust me.