From my experience with men, the more a man has sex and orgasms in a short period of time, the smaller his loads gets. The first orgasm is always a large load, then second is lesser and so on. I don't think that it's only an impression I have, I had this confirmed by many men.
So why according so much importance to the size of your load? Really?

As a woman, some days, I can hardly lubricate, some days I get wet, some days I squirt a small amount of fluid and then there are days where I can get the mattress soaking wet... it's not bothering me! I'm not always looking to improve that. It's the way a human body works and I accept it!
I know some men have that fantasy of seeing their loads all over a girl's body but besides that, the amount of sement you are squirting should be irrelevant. It is proven that some men have orgasms without even ejaculating and some men ejaculate without having orgasms. If it's the strong orgasm feeling you are looking for, why not just get a prostate massage?
My only advice : drink a few litres of water per day. It must be like anything else, the better your body is hydrated, the more "fluid" your body will produce.
And while you are at it, eat some pineapples to give it a good sweet taste.
I doubt any of the "grandmother's theory" on producing more sement works... Wasn't BrunoB selling some pills to shoot bigger loads?... I doubt that works too.
** For the ones who think it's cool to perform as if it was a pron flick, just so you know, even in porn flicks a load isn't always a load... I've see handsoap used, I've seen eggwhites, yogourt mix with water etc. No, these guys are not above average humans, nor are they more masculine... it's only a movie! **
Anyway, good luck!