The main technique people say works for this is called edging. Basically it’s prolonged masturbation. Most people say that what you do is jack off hard until you’re about to bust, then you stop, squeeze your pc muscle if you want, let it subside, then continue again, for a significant amount of time - maybe half hour or so.
I’ve been doing this, but I have a different theory. People say that the point of edging is to train yourself to stay aroused without ejaculating. I think it has more to do with the head of the penis, and how sensitive it is. If you’re used to jacking off dry, only touching the shaft, then when you start having sex, the head is so sensitive, it’s a trigger that causes you to bust right away. I think this is what happened to me, and a lot of guys.
So the important part of what I’ve been doing is using lube - using astroglide cause my girlfriend got some - it’s ok, maybe you know of a better one. Anyway, what I’m trying to do is really stimulate the head (well, the whole thing, but with the emphasis on the head) so that it stops being a trigger for ejaculation. It seems to be working. At first, I would be able to cum really quick when really lubed up, Now, not - and it’s only been like a around a couple weeks. I really try to stimulate the head, sometimes rubbing my palm around it to get the tip in mid stroke. Unfortunately, I can’t be positive this is working, cause I’m not having any sex right now. I wish I were, cause I think it’s really working. Give it a try for me, won’t you? If you’re gonna keep on banging your chick while you do this, try extended pleasure condoms. They’re awful - you don’t feel anything - but you’ll be able to have sex without busting early and ruining your progress.