The Big Fight
Everything your hero and villain do is leading up to the big fight scene, the climax of your book. In this scene, there is one extremely important rule to remember:
Do not pull your punches.
If your villain strikes at your hero, let your hero get hurt. This proves that not only have you created a villain who is strong and vicious enough to mean business, but just as in the real world, if you fight, you'll get hurt. Writers who pull punches because they don't want to hurt their favorite characters are only doing their readers a disservice. There's no threat in a world where your hero can't be touched, and that makes for a dull book.
Let your villain fight in character. Is he smooth and polished? Make him fight that way. Is he a bloody-minded man of chaos? Show that. The same goes for your hero, by the way. What you'll have by doing this is a fight as unique as your characters.
Another important rule: Your villain must lose.
Seems obvious, right? But in the romance genre, this is a must-happen, just as is a happy ending. Let that bad guy get his comeuppance so your reader can cheer with your hero!