I find fingers tickling the opening of the vagina and all around the U-spot is key while performing oral. That's a good way to warm them up as you begin on their clit when you get that far. Massage her breasts and stomach and thighs with your free hand. This technique will get her wet quickly and started on the incline toward orgasm. Wait to insert a fingertip, and then a finger, and then two fingers, and then eventually start on her G-spot with the come hither stroke. When she's going, add pressure to the top of her G-spot on her tummy above her pubic bone and go to town on her clit, sucking on her pussy and licking hard, putting the whole thing together. Alternate with your fingers in deeper to her A-spot from her G-spot. Also rotate your hand palm down and press down firmly deep in her vagina close to her cul-de-sac.
Pay attention to her body language and go with her flow, and she'll get there.