Try to keep it area-specific. Guys generally have no patience for empty compliments. Instead of telling him he's handsome, try saying something like, "That shirt brings out the blue in your eyes".
Telling a guy that he looks good when he knows he doesn't is a sure way to get designated to a lower species of female. If you want him to feel warm inside, tell him something true like, "I love what you've done with your hair today".
Compliment him on what he works on the most to get the best results. For example, you can compliment him on whichever part of his routine you think he pays most of his attention and cares about.
Try not to offend him by complimenting him on his grooming habits. This makes them feel fussy and feminine.