Each person pattern of orgasm varies from one another. You have
to discuss with your wife about her favourite positions and other
stuffs that will make her highly to achieve an orgasm, that is
through intercourse I'm talking about.
Perhaps you might try to have a longer than usual foreplay, not
limiting to touch, but as well as words. Whisper sweet, sometimes
naughty, words in her ears to arouse her. The idea is to make her
almost there, so during making love, you stand a higher chance. Of
course, sensual words and touching do not stop there, while doing
it, continue your foreplay.
Another way is to use the commonly method 'stop-and-go'. Find out
your 'point-of-no-return', and stop all activities, wait for the
feeling to subside, then continue. However this is not a sure win
situation, as some women may feel discourage and even losing
patience when you stop many times. Still, you can discuss with your
wife about this.
I've heard of another method which is using your sphincter muscles
to control your orgasm. That muscles is in man's groin area, and we
actually used it everyday...to control the urge of urinating.
Likewise, it will prevent you from ejaculating. It requires
training though to effectively use it.
Your wife can do her part as well, by sitting on top of you. That
way, she can actually rub her clitoris against your pelvic bone
back and forth. Strictly speaking, you are not moving nor
thrusting, so the urge of cumming may not be that immense. Till she
satisfies, then change position and finish on a happy note.
Again, what matter most is that you should openly discuss this with
your wife. Do not be afraid to let her know. Work everything out.
There are a lot of articles on the net that can help you, I'm only
telling you from what I know, there may be more. Do it healthily
and lovingly.
Cheers.