Start with a story about a romance. You can do a historical couple, someone you know who has an interesting love story, or a personal story you have about love or Valentine's day. Another way to start this essay is to use what I call "Reversed Expectations." Start with what is expected about the holiday, or what you were expecting on a particular Valentine's day and then tell what happened to reverse those expectations.
The body of your essay can be a story about Valentines, reasons why you do or do not like this holiday, explanations about how people celebrate it differently around the world, a discussion of the history of the holiday, description of how it has become a major commercial holiday, or a discussion of how important this day is for certain businesses like florists. Conclude with what the holiday means to you, why you do or do not like the holiday, or what you think should be done to make this holiday better.