A music system
It doesn't have to be fancy surround sound (bonus if it is), but music sets the mood, is a good talking point and fills in any gaps in conversation. Create a mellow playlist that can take care of itself.
Book shelves with actual books
The books you own offer great insight into what you're interested in and show that you might potentially be interesting to her. Bonus, if your shelves also include well-placed trinkets from your travels
A wall with interesting art
This could be a favourite framed photo, paintwork, wallpaper, or just some exposed bricks – atleast it shows you have some taste. Art of some sort is a compelling expression of your personality, which can make you more compelling. See how this works? Yes, even the cavemen daubed paintings on their walls to make them homely.
If your tiny flat can’t fit a furry friend a plant is your next best bet. It shows that you can care for something aside from yourself – a good sign for any budding relationship.
Porn on display
You would be surprised how often guys either leave their stash out by mistake, or worse, on purpose in some sort of alpha-male man-cave display. Watching porn does not necessarily make you a better lover. She knows this. In fact, seeing it kind of makes her feel sorry for you and your single-handed show. And if you won't do it for her, spare your mother.
Game consoles, cords, paraphernalia strewn all over the floor
It's great to have a hobby. But in the beginning let her live with the hope that it's reading to orphans and writing her poetry. Gaming, whether correctly or not, implies losing you for hours in front of the telly while she trips over your gaming cables. (FYI anything strewn over the floor also implies you can't pick up after yourself.)
A funky couch
What a wasted opportunity! You want her to sit, stay, relax, cuddle up to you during a movie, make out with you – not such a pleasant prospect with crumbs in the creases, miscellaneous stains and an unpleasant odour. Er on the side of caution when it comes to overly-masculine leather couches though – even thought they're easier to clean. But sometimes form trumps function: they can either be very cold or sticky, or worse still, you end up sliding off.