You're looking for the area around the g-spot, so the front wall of the vagina. Have her on her back, possibly reclined rather than lying flay, your palm facing up and fingers curved. Make sure she's aroused before you start, and you're feeling for a slightly fleshy lump. The best techniques are either 'windscreen wipers) so fingers moving side to side over that area, or stroking downwards (as if doing a 'come here' motion with your fingers).
Toys are good too. My favourite is one called the njoy wand (stainless steel, I have a pic with it on my profile) but any curved dildo will also stimulate that area.
Expect a small amount of liquid at first, not much comes out of the skene's glands and when there's more liquid it's either combined with pee or it's just pee. She will start to produce more liquid as she becomes a regular squirter though.
Don't expect it to happen first time, but keep going with playing with that area and both relaxing and I'm sure it'll happen eventually. Please, keep us posted x