Summarize the following:
No matter what he says or how he acts about it, your boyfriend (like everyone else) appreciates hearing nice things about himself. We all seek validation for how we look and what we do, especially when it comes from someone we care about. It's good for your boyfriend's ego, his pride, and his happiness. Don't make this more complicated than it needs to be. If you like the way he laughs, tell him. If you like the way he styles his hair or treats strangers politely, tell him. If you can compliment him on something you know he really cares about, like his basketball skills or his math grades, all the better. Relationships are hard work, and require effort from both parties. Take note of the things he does for you and for the relationship, and let him know that you do notice and are thankful. Does he work a second job so he can take you out on nice dates or save money for an apartment? Does he go out of his way to pick you up so you don't have to walk home in the rain? Is he nice to your mother? Specifically say to him "I appreciate that you do [this thing] for me and for us." Even if you have a guy that isn't big on public displays of affection, there are always subtle ways to let him know how you feel. Actions usually speak louder than words when it comes to demonstrating affection. Hold his hand, and kiss him for no good reason. If he's not the hand-holding type, let your hand brush against his from time to time, and maybe just slip him a quick peck on the cheek. Even most modern guys like to feel like protectors, so putting your head on his shoulder or sitting on his lap is a good way to create a sense of him protecting you with his embrace. Simply spending time together is great, but make sure that you are putting your focus squarely on him for at least some of that time. That means putting your phone down, looking him in the eyes, and listening, talking, or just letting him know you're there. Make your time together quality time something you both enjoy and will remember. Life is busy and only seems to get busier, so don't take your time together for granted. Go on a surprise day trip. Take a surfing lesson together. Just sit and talk with no distractions. According to esteemed relationship researcher John Gottman, healthy relationships tend to have a ratio of at least five positive interactions for every negative one. The more often you show interest, concern, appreciation, and affection, all of which start by paying attention, the better your odds of reaching the "magic number" of positive interactions.

Summary:
Compliment him. Tell him you appreciate him. Display your affections. Give him your attention.