Try the condoms that make you last longer (they cut down the sensation on your penis so you can last longer).
Change up/slow down the speed and depth of your thrusts to help you calm down if you start to get too excited.
If need be, pull out and go down on her or finger her until you can get back in.
And as silly as it sounds, "think of baseball" lol... or anything to distract you from time to time to help take the edge off when you're getting close.
If you are trying to last longer so that she can have an orgasm, try doing a ton of foreplay so she's already close before the sex.... then it won't take her as long once the sex has started. Or give her an orgasm before sex.
On Your Own:
Practice with yourself and get yourself close to finishing and then stop. Keep doing that to extend the time you can last. It will be fun and productive!
You can also look into doing kegel exercises.
If none of this works and you think you have a problem with premature ejaculation, there are medicines that can remedy it if it is for a physical reason, and sex therapists to help if there is an emotional cause.