Go down on her

You figure if the goal is to make Nicky cum, you better get her as turned on as possible. Reaching her, you kneel down on the floor in front of her and put your face between her spread legs. Inhaling deeply, you take in her musty scent then glide the tip of your tongue up the length of her slit. Nicky shivers beneath you as you reach her clit, exhaling the deep breath she had been holding in. You continue lapping at her, licking her like you would an ice cream cone, savoring her lightly tart flavor. She runs her fingers through your hair, holding your head against her crotch. She wasn't lying when she told you how wet she was and it doesn't take long before your chin is coated with her juices.

"Ooooh... Uh-huh... Yeah... Oh, right there! Right there!" she moans out as you begin sucking her clit into your mouth.

Moving a hand up between her legs, you slide two fingers inside her slick hole and curl them up inside her, finding the soft, spongy tissue of her G-spot. Keeping them buried inside, you move them back and forth illiciting further moans and groans from Nicky's mouth. Her enthusiasm is contagious and any doubts you may have had before, are dispelled, with you more than happy you've made the decision you have. By this point, it seems as though you've done enough to arouse her fully and are more than ready to get inside your girlfriend's hot, little sister.