Squirting has become this Holy Grail of sex these days and everyone seems keen to see if it can be achieved. If the Forum topics are anything to go by, every woman should be able to squirt but it's the technique that gets them there.
Physiologically, all women have the small ducts near their urethra that can gush small amounts of fluid at orgasm and it seems the sort of orgasms that encourage this gushing involves stimulation of the good old G-Spot.
Therefore, the best thing to do is experiment with your partner's G-Spot to see if her reaction differs according to how you manipulate it. I think some women find G-Spot stimulation enough to orgasm from, but most will still need clitoral or other stimulation at the same time. At any rate, the orgasm felt through G-Spot stimulation should differ to some extent and there is a sensation of having released urine but in a more pleasurable way of course.
As for the fluid, don't focus on it too much. The jury is out as to whether big gushers are actually gushing the duct fluids or urine, or both.
I did mention that technique is key but just as crucial is your partner noticing changes in her reaction and arousal with G-Spot stimulation. To some extent, it might help if she perused some G-Spot oriented adult toys and have a go on her own too.
Definitely do a search in Forums as there are many ladies who have had the pleasure and are pleased to share their findings.