How can I get closer to my boyfriend's mother?

You just have to be yourself! If you think you're really off the bridge with your personality, just pull it back a little. If you had a son, how would you want his girlfriend to be acting around you? Think of yourself in other people's shoes, and imagine how they would react to the situation. Act cheerful, but not sarcastic. If she tells you something sad, be compassionate and sympathetic, but not sappy. Ever hear the saying, "anything in moderation?" Take this advice for your personality. You could try gliding by an evening with just small-talk and compliments, or start off with that and then talk about more personal things, such as your childhood, school, etc. Don't be afraid to be yourself, though. Good luck, and don't worry!