3. Be prepared.
If you're spending any extended amount of time with his family—whether just a long evening or a few days—dress comfortably enough that you can go with the flow if the occasion calls for it. An after-dinner walk with his 'rents will be even more uncomfortable in sky-high heels. And a lively game of charades? His little brother doesn't need to see your crack wriggling out of your low-rise jeans.