I struggle with the same thing! Find out how he best receives love first - does he need to hear "I love you"? Does he see it when you keep the house clean? Do you need to buy him a gift? If he feels the most that you love him when you hold his hand or he gets alone time with you, then you telling him how handsome he is in his blue shirt probably won't come through well.
Someone once told me about a book they read on how to find the right love for your partner. If I remember right, they will find it the most either in words that you say, actions you perform, the touch he feels, the gifts you give, or the quality time you spend. So however he feels your love the most, you can follow through with that and let him know you do it because he's perfect for you. An example in my life is that I hate housework and when I come home from a busy day I just want to spend time with my boyfriend. I find time, however, to do the dishes and a few loads of laundry because I know he's the type to see my love through my actions and I know what it means to him. And I am big on touch, so him spontaneously giving me a neck massage or holding my hand without me holding it out for him shows me how much he cares. Once you find how the other feels love and really work at it, you will notice a serious change - I hope this helps =)