If you don’t know what the girl wants, be gentle. If stimulation is too subtle it can still be exciting, while too rough is frustrating.
Don’t move too quickly. A good lover takes time. First kiss and caress her thighs and belly. Go slowly and wait with her genitals until she practically forces you to lick her lips and clitoris.
When you’re ready to stimulate the clitoris, don’t start licking immediately. Start with the area around the clitoris. Run the tip of your tongue between her outer and inner lips and around the clitoris.
When you do the top and sides of the clitoris some girls like a pointed tongue, but when you stimulate the more sensitive underside this is often too much. Then you need to let your tongue go soft.
When the girl gets very excited, approaching orgasm, it’s very important to maintain your rhythm and pressure, and to make predictable movements. If you keep changing position and the kind of movement she’ll not come.