Girls differ greatly when it comes to oral sex. Don’t assume she’ll like the same things that drove your ex wild. So ask what she wants. Some possible differences:
Often the clitoris is too sensitive for direct attention, especially when a girl is not aroused. You can stimulate it indirectly by licking the inner lips, the clitoral hood from side to side or by licking to the right or left of the clitoris.
Some girls like fast movements, while others like to be licked slowly. Some like a lot of pressure, while others find this too much.
When it comes to the clitoris some girls have a favorite side or spot. So try different things till you hit the hot spot.
Some girls like vaginal penetration during oral sex, while others find this a nuisance. So don’t just stick your fingers or tongue in her vagina, but ask if she likes this. If she does, ask her if she wants you to hold your fingers still or twist, jiggle or thrust them in and out.
Most girls want you to continue stimulating their clitoris during orgasm. However, for some girls this is too much of a good thing. They prefer general pressure: the mouth enveloping the vulva.

If you don’t want to ask what she wants, pay attention to her body language. For instance, she might move her pelvis closer or further away, move it to the right or left, reposition you or guide your head. This can give you the information you’re looking for.