There isn't one answer that will work for everyone, but here are some ideas to get you started:
-A heartfelt letter telling your boyfriend how much you love and appreciate him
-A homemade card or gift expressing your affection in a creative way
-A luxurious present likeTickets to a show or a fancy dinner
-A simple but sweet gift like flowers, chocolates, or a heartfelt note
-A fun activity together like going on a romantic hike or picnic
Whatever you do, make sure it comes from the heart and is something your boyfriend will appreciate. Most importantly, have a happy Valentine's Day!