It's important to play with the prostate as it is a literal toy. There is a pleasure button buried in the roof of a girl's hole, and playing with it like a toy yields marvellous results. I have three ways I like to play with her prostate: Rubbing, Pressing and Thrusting.
Rubbing is self explanatory and also the best for warming her up, methodical clockwise gyrations are very welcoming - you can however, once she's warmed up start to alternate between clockwise and counterclockwise or start to focus your gyrations on slowly easing her hole open.
Pressing can manifest in either hard consistent pressure or a series of firm taps. Varying between the two is fun of course, overstimulating her with fast and strong taps before turning her brain off with one tap that doesn't stop is a classic.
Thrusting is obvious, and is honestly more stimulation for the hole than it is the prostate - with deep enough thrusting and an open enough bottom you can also start to tease her second hole and gently tug on it if she enjoys the sensation (or more if she really enjoys it).
The combination of all three of these techniques is what gets a girl to see stars in my experience - add and take away and try to keep her at the "limply holding on" phase (my girl starts involuntarily confessing her love at this stage). Once she goes away completely (I've heard this called the Forever Place) she's likely to cum when she returns if you've done it right, a countdown can further establish your control over this involuntary response from her body.
Another fun technique is gently squeezing her prostate between your thumb on the outside and forefinger(s) inside. If she becomes accustomed to this feeling you can even start to rub her prostate from the outside whenever you'd like (just about on the underside of her taint) this has the added benefit of feeling for both of you remarkably like you are rubbing her pussy.
With all these techniques in hand you can (in my experience) blow a girl away with a single finger, but keep in mind that different numbers of fingers give different experiences - a single finger can offer laser-focused precision to pleasure points, two fingers can keep the entirety of a prostate entertained and three or more can be spread to further stimulate the hole (and invite more inside).
Have fun and chase whatever reaction you best want from her - each girl is different and once you learn the language of her pleasure you can start to do things she may have never thought possible. Remember! The prostate is a toy!