Make sure your nails aren’t too sharp and don’t have rough edges, ruining the pleasure.
When you buy condoms buy some water-based lube as well. It’s always good to have this at hand when you expect to have sex with a girl. If you don’t have lube, use plenty of saliva or her own juice. Never finger a girl dry.
Be careful with inserting one or more fingers in the vagina. Ask her first if she likes to be penetrated, because many girls won’t appreciate it. If you don’t want to ask first try it with one finger, just two inches in. Her body language may give you the information you need.
When you finger a girl you can let the pal of your hand rest on her mons. This is less tiring and increases the chance that your movements will resemble her own when she masturbates. But make sure you don’t move the palm of your hand too much, just your fingers, otherwise the hair on her mons will irritate the skin underneath.