The three musketeers
Lie next to your girlfriend, your arm resting on her body and your hand between her legs. Push her inner lips to the sides with your index finger and ring finger, stroking the inside of her lips with your middle finger. Wet your fingers with saliva or a water based lubricant before you start, making sure it’s slippery.

Digging a hole
Sit next to your girlfriend, with your head in the direction of her feet. Lay the palm of your hand between her legs, the tips of your fingers past her vagina, but not touching her anus. Pull your hand upwards, towards her belly, while your finger tips separate her inner lips. When your hand reaches her belly you make the same movement with your other hand. It’s like a dog digging a hole, but in slow motion. Don’t forget to pay attention to the clitoris and use a lot of water based lube.