One thing that adds tremendously to a guy's handsomeness is believe it or not, his eyes. So next time you look into those deep caramel, sea blue, etc. Eyes, you could say "You have such gorgeous eyes". Then kiss him! How romantic!!!
Also, in a lot of relationships the girlfriend is "in charge". Kind of like the leader of the relationship. Normally the girlfriend plans what they'll do together, when they'll do stuff together, what they'll wear together, etc. So when a guy gets complimented on the shirt that he picked out or something that he did on his own, it boosts his self confidence and makes him appreciates that he has such a great girlfriend.
Also, in a lot of relationships the girlfriend is "in charge". Kind of like the leader of the relationship. Normally the girlfriend plans what they'll do together, when they'll do stuff together, what they'll wear together, etc. So when a guy gets complimented on the shirt that he picked out or something that he did on his own, it boosts his self confidence and makes him appreciates that he has such a great girlfriend.