I had some luck with this and kind of accidentally did it when masturbating. I thought I had peed, but it didn't smell like pee and when it dried it was white. After then I would try to recreate the situation and here's what worked for me:

1 - Relaxing: I had to relax and really allow myself to feel
2 - Focus on the G-Spot: I know exactly where mine is, if you don't spend some time with some pressure in there to find out, for me it's necessary to have that type of orgasm.
3 - "Push" - in the beginning, after I realized it, it felt like I was holding some pee in. I recommend you actually push like you have to and it will help you let it out.
4 - Get some help: a boyfriend/lover using his fingers, pushing (or using the come here motion) on/over your G spot (on the roof of your vagina). If you don't have to think about your movements and you can really focus just on letting go and having an orgasm.


Remember that not everyone can have this type of orgasm. Just trust your body and enjoy whatever orgasms you can have. Otherwise, just have fun with what you got and have fun searching.