A woman (or anyone with a vulva) may find it arousing if you spend some time kissing and touching her upper thighs and the area around her vulva (genitals) before oral sex.
The whole genital area is sensitive, but for most women the clitoris (with its 8,000 nerve endings) is the most sensitive part. Gently part the outer lips of the vagina and look for the vaginal opening, and the hooded clitoris just above it.
Start off softly, using a relaxed tongue to make slow movements and work up to faster movements with a firmer tongue. You can try moving your tongue in different ways and using different rhythms – ask your partner to find out what she enjoys most.