Unless you're a rare unicorn of a male specimen, you'll likely be less opinionated about the decor than she is. She'll probably take the lead on designing the place, having already watched months worth of HGTV and devoting several Pinterest boards to each room of the house. Be kind and flexible. Assert your opinions, but be prepared to cave to her just for the sake of maintaining your sanity.
Again, compromising is key. Your 300-strong video game stash can come with, but don't expect her to be cool with keeping your beer bottle collection. She won't care that you've been working on it since college. Those rare lambics are going in the trash.