Grab the lube.

You take the bottle of lube and squirt a small amount onto the tip of your finger. You begin to circle around her asshole, and she groans as your finger slides in past her tight pucker. She lets go of her ass cheeks, and you feel her tighten up around your digit. You have no idea how something so tight is going to be able to take your cock. She lifts her hips up to present her ass higher into the air for you, and her hands are already between her legs, rubbing the insides of her thigs as she spread her legs a little wider.

You reach the maximum depth of your finger, and slowly drag it out before pushing it back in. Her ass clenches around it but provides little resistance for your lubed-up digit. You watch as a thin trickle of juice leaks out of her pussy and runs down the inside of her thigh. You slide your finger in and out for a few moments, and once you've got a sense for her tightness you drag it out and line yourself up behind her. You squirt lube all down the length of your cock and begin to rub it in until your entire shaft is glistening. Finally, the moment arrives, and you press the tip of your cock onto her waiting asshole.

Slowly you put pressure until your head breaks through her sphincter and settles the first inch of your cock inside of her. She gasps as your tip splits her open, and her hips begin to tremble. She reaches back and grabs the wrist of your lubed-up hand, and pulls it forward to the rear of her head, urging you to pull her hair, You run your fingers through her silky black hair before taking a firm handful and pulling tight. She arches back until her spine is bent backward, and only her ass is bearing the weight of what is to come.