Admire your partner's strengths - and overlook the little things.
Every day, tell your partner how much you admire one of his strengths. Say, "I'm impressed by your patience with others," or "You are such a good cook." Everyone likes to feel appreciated, and sharing good thoughts will have a positive impact on your relationship and your partner's self-esteem. Make sure the quality you highlight really is a strong point, however, or he might doubt your sincerity.
On the other hand, accepting the quirks about your partner that drive you nuts will also go a long way towards enhancing a romantic relationship, as long as it's not a destructive behavior like driving too fast. Some traits that can be endearing when you first meet someone -- like the way he or she wears a certain T-shirt every Saturday or constantly misplaces his or her keys -- can be annoying when you've been together for a while. Be willing to overlook those pesky behaviors; after all, that's what makes your sweetie unique.