Do Your Research
Maybe your boyfriend is the only thing that you have in common with his parents, but you should make an effort to remedy that before meeting them. Of course, you'll need to pump your boyfriend for lots of information. Ask how his parents met, where they grew up, what they do for a living, what they like to do for fun. With any luck, you can find some common ground with them. If his mom is a big history buff, you can mention that you minored in history in college. That might spark a whole discussion about favorite historical sites or books. If Dad grew up in Chicago, talk about the time your family took a vacation there.
Even if you can't immediately connect with something about them, you can do a little research on your own so that you can ask questions to get his parents talking. Most people like talking about their interests with a little prompting.
Also, ask your boyfriend if there's anything especially important that you need to know. If his mother is very particular about her white carpet and insists that all guests take their shoes off at the door before entering, you'll be prepared.