1. Wash your hands. Make sure to wash your hands prior to touching your partner’s vulva, to avoid exposing them to any bacteria you may have accumulated on your hands throughout the day.

2. Warm up with foreplay. Foreplay—like making out, dry humping, or massaging—will build up anticipation and allow your partner time to become fully aroused, making fingering much more pleasurable. It can take about 20 to 45 minutes for your partner to become fully aroused. When you're ready, make sure your hands are warm. Start by stroking the inner thighs and applying light pressure to the mons pubis before exploring the vulva.

3. Use lube. Lube can make almost any sexual activity more pleasurable, including fingering. Many vaginas secrete their own fluids that can be used as lubrication, but your partner probably won't be fully lubricated right away. Use your hands to gently apply lube to all the parts of the vulva. Keep things juicy by applying more lube as needed.

4. Get to know the clitoris. Start off with indirect stimulation, using an up-and-down motion to slowly rub the area between the outer and inner labia, then move up to the clitoral hood. Flatten your index and middle fingers, then move them together in a circular or side-to-side motion. Some people like direct stimulation of the glans (or nub) of the clitoris, while others find it too intense, so it's always a good idea to start with slow, indirect clitoral stimulation.

5. Explore the G-area. The G-area, also known as the G-spot, is located a few inches inside the vagina, on the front wall (belly button side). This area swells when your partner is aroused, so wait to start G-spot stimulation until after clitoral stimulation. To stimulate the G-area, lubricate your index finger, then, with your palm facing up, slowly insert your finger into the vagina, about one to two inches deep. Curl your finger in a come-hither motion, looking for a ridged or wrinkly area. Once you've found an angle and rhythm that works for your partner, you can reincorporate clitoral stimulation using your other hand, a sex toy such as a bullet vibrator, or your mouth.

6. Add the anus. Don't limit yourself to the vulva and the vagina. Try stimulating the anus and perineum (area between the vagina and anus) if your partner is open to it. Start by applying lube to the perineum, then circle the anus with your lubricated finger. Your partner may eventually want the tip of your finger inside their anus, or more, or they may prefer you to stay on the outside of the anus while stimulating their vulva.

7. Check in regularly with your partner. Every person finds different things pleasurable, and different fingering techniques will work better for different partners. Make sure to regularly check in with your partner to make sure that what you’re doing feels good for them.

Source: https://www.masterclass.com/articles/how-to-finger-a-girl