Don't Move Too Fast or Too Slow
Along the same lines, you don't want the action to move so fast or so slow that readers get confused or bored. Although you want details in your story, don't focus too much on insignificant ones.
At the same time, you want the action to flow at a normal pace. Don't change scenes too quickly. You need to allow time to build up to the sexual act. You shouldn't be talking about sex in the first sentence or even the first chapter of the book. Lead up to it. Allow readers to anticipate it.
{relatedarticles}
Use Dialogue
A successful work of erotica includes lots of action as well as dialogue. The people involved need to be talking. They can't just meet and have sex right away. Dialogue sets the mood and shows the character's personalities.
Plus, dialogue can make a naughty scene even naughtier, or a silly one even sillier. Also, don"t be afraid to use metaphors or double-entendres. These are when you say one thing, but mean something else (like sex). It works as verbal foreplay, building sexual tension until the main event (the actual sex act).