It is always about the value you provide to him

From a boss perspective, he values most who can help him. The good thing is that he knows exactly what you are doing, so if you are doing good he knows. Ask questions when you need to, but always try to find some solutions or suggestions first. Then it becomes a discussion with him. If you have some great points, then he will value your input which leads to your relationship with him getting close naturally. Do not force anything as he know as well. If he is a nice boss, your relationship with him should be pretty easy. Be nice to him, but not because you want to take advantage of something - rather you are a nice person naturally.