few things
say her name often
lock fingers with hers
don't ignore any part of her body with your mouth or your hands - especially the small of her back, along the spine, shoulders and neck
touch her neck and face with your hands - especially while the other hand is wrapped around her, on her thigh, etc
kiss a lot - and don't use your tongue everytime - ever watch 2 girls make out? they don't go overboard with the tongue, especially at first