Partially, reading a lot of erotic works. I've been reading erotic writing for a long time, and reading a variety of erotic stories has influenced how I write my own. When I'm writing them, I try to convey how the character is feeling as well as the actual action that is happening. And I especially want to convey the loss of control that can come with sex and sexual situations, the way hormones and instinct can take over, the gleeful disorientation... I really like writing erotic scenes, though it stresses me out to do so.