In my apartment (2/2 1200 sq ft) I ended up buying a plastic/fake tree and had enough room to put it in the living room. I themed it out with silver and white lights from Home Depot. I have a balcony so I was able to put lights around my balcony and had a timer that would shut off at 2am (Home Depot). For my apartment door I had a door cover that looked like this
. I bought it at Party City for real cheap like $5.00. Like some people said just the small things can do a lot like; Christmas pot holders, candle sticks, pen holders, table runners, coffee mugs and door mats. Also don't forget the mistletoe on top of every door ha. If I think of anything else I will let you know.
PS: make sure your complex approves of Christmas decorations... I know how some places work and they may deny decorations