You wanna manage a few things so everything is set fine for the purpose:
the environment undisturbed, nobody around who could disturb you, at all, not even coming home (or whatever else) for a few hours for sure
your state of mind calm, relaxed, balanced - if you are a stressful, anxious kind of person then try to set your mood to the pleasure time, you just wanna relax, have fun, enjoy it - nice, beautiful music you like and keeps you smilin can help a lot, and books and movies, videos you enjoy too, especially the erotic kind
you don't wanna rush, you don't wanna force anything, it's best to start to read or watch something, and take your time by caressing yourself very longly first
you wanna go step by step and slowly, the best is when you can't hold on anymore and wanna go on to the next level - but don't wait too longly, my experience is that when I wait too long it's hard to get back into the mood physically again, as your focus can get tired too, so you wanna follow yer desire, but stretch it as long as possible
and of course you wanna please yourself in every way you enjoy it, no matter if you find a position which looks funny, or if you have a fantasy what others would find ridiculous, it is yours, nobody sees you, nobody can laugh at you, go for it, and enjoy it, that's why you are doing it
and it's a good thing to stretch your arousal too, not coming so fast, though you can go for it
focus on yer clit, arch your muscles, but don't tire yourself too much as well - even while you're having a quick break keep on exciting yourself lightly
some more good advices, by personal experiences:
make the temperature good, it sucks to stop and get warmer or cooler
look sexy, it feels even better to feel that you are a delicious sight in your pleasure
eat and drink if you haven't for a long while, you don't wanna stop because of such a silly thing
same goes for other bodily functions, go to pee, better to do it before you start, cause if it takes hours you don't wanna stop in the middle of it because of such a discomfort
and of course what we all know already, use toys, any toys you want, better have many of them around, cause batteries and charges can go low in the hours of pleasure, you wanna have plenty of power handy...
If you want to achieve ultimate pleasure with your mate (I mean your precious chosen one, I just like to call mine my Mate... ^^) then you wanna ask him to set his mind ready to put all his heart into it and be willing to spend hours with pleasuring you, focusing on you fully, and you also wanna tell him in the process what you like and what not, you wanna dare to speak up, and ask him to do everything for you to help, I do believe that it will work cause, blah, just because I think that you have a wonderful loving mate (hopefully!!!), and with such a precious one everything is possible!!!
I read encouraging things in yer profile btw, but if you still couldn't make it, well, I wish the best luck with it, and dare to shoot a message whatever you wanna ask or tell, I do hope that this is a good initial walkthrough in a nutshell for anyone having similar troubles...
It takes a while but sooner or later it happens and one learns how to enjoy life fully, the key is open mind, and a lot of patience, with them nothing can go wrong...