Get her ready with lube

You squirt out some lube on her ass crack, then a little more on your finger. Then, you pull one big, round cheek to the side and gently swirl your finger around her pucker. She inhales sharply. "Shiiiiitt," she says through her teeth. You prod at her anus, pushing more lube in around it, and she reaches back to pull her other cheek aside. "Put it in," she begs, and you start pushing your middle finger into her ass. Callista wriggles, humps, and grunts as you gently finger her, kissing her lower back and ass while you stretch her open.

After a while, you work up to two fingers, pumping lube well inside of her. "I'm ready," she tells you needily.