This one mostly applies if you're invited over for dinner at your boyfriend's parents' house. When you arrive, don't just park yourself on a sofa and hang out, waiting to be called to the table. After the initial pleasantries, ask if there's anything that you can do to help. Even if you're not a cook, you could wash or chop vegetables, fill glasses, set the table or help carry the food to the table. They will probably say no initially, but try to let them know that you'd really enjoy helping out.
If you're offered a cooking task that you're unsure about, ask for direction or admit that it's beyond your skill but you'd be glad to do something else. You don't want to be the one to burn the entree. Helping out in the kitchen also gives you a good opportunity to make small talk. It's easier to do if you're engaged in a task rather than just sitting and fidgeting. After dinner, offer to clear the table, load the dishwasher and wash or dry the dishes.