Try this every day or so for several weeks - this will
1) give you stamina
2) teach you the signs of reaching the "point of no return" where you are going to ejaculate no matter what. Once you know those feelings you can pretty much control when you ejaculate.
Set a goal of masturbating for 15 minutes without ejaculating. Try getting really close to orgasm a couple times, but don't go all the way. If you get close to orgasm, stop stimulating yourself. Start again when it is "safe".
When you hit 15 minutes, reward yourself and have an orgasm.
Use lube so you get all the sensation that your penis has to offer. Use one that won't dry out - albolene, olive oil - so you don't have to keep applying it.
Don't watch porn, as the porn will distract you from what you are feeling. If you want to watch porn until you get hard, that is ok. But turn it off, and just focus on your own feelings.
If you blow a load before 15 minutes, no problem! Just enjoy it and try again tomorrow.
Once you have mastered 15 minutes, up your goal time to 30. Also try to come close to orgasm at least 5 times without going all the way.
Once you get to 30 minutes you will be pretty much able to last as long as you like with a partner.
