1) Donate $50 (or what you can afford) to a domestic violence shelter. You've probably already seen the campaign for #50DollarsNot50Shades. The Fifty Shades of Grey movie is coming out tomorrow, and advocates for abuse victims charge that the film glorifies emotional manipulation, stalking, and violence as "romantic." They're urging people to forego the movie and donate the money they would have spent on the movie/dinner/popcorn to a domestic violence shelter instead.
I myself have not read any of the Fifty Shades books, although the online summaries I've seen are pretty damning. Regardless, the money is for a good cause.
2) Be prepared. True, sex doesn't "just happen," but it's certainly possible for people to get caught up in their emotions—especially on a holiday that's dedicated to celebrating exactly that. So if you're in a relationship, have a conversation with your partner ahead of time about your expectations for Valentine's Day. As applicable, remember responsible condom use. (Unless, of course, you're trying to conceive, in which case we wish you the best of luck!)
3) Invite your friends to like Secular Pro-Life on facebook. Our goal is 7,000 likes by the end of Valentine's Day, and we're just a few dozen away!