In a space that's a little on the small side, consider hanging a bunch of very similar pieces of art to help fill the space and make it feel larger.
Ok the next photo is a little overkill in my opinion, but still not bad to look at. I think the antlers and branches on the table are a bit distracting from the simple symmetry that could've been created.
Ok let's talk about gallery walls, which could be related to the topic above. But the vignettes above are simplified to not overwhelm an already tight space. A gallery wall really has no rules. I like to get a good mix of art, like maybe an abstract, some photography, mixed with some words. I sometimes like to lean all these different art pieces on a ledge for a super casual look.... See below
So maybe you don't want to go quite as casual as the photo above. You can still create a killer gallery wall! Aside from mixing up the type of art, throw in a clock or mirror. Be deliberate about how you're going to handle the frames and mattes. They don't need to all match, but make sure there isn't just one odd man out. Ten black frames and one wood frame might look like a mistake. Just be aware of the details because they really do make all the difference
Now that I've gone on about clusters of wall art, let's take a minute to talk about negative space. When you have a well accessorized room, it's important that your eye has a break. I truly believe negative space can impact design as much as a decorated space.
The last thing I'd like to go over is hanging heights. Nothing screams bachelor pad like a bunch of super high pictures (most likely of Bob Marley). You want the art to be at eye level, but because that can vary so widely, 63" is thought to be a good midpoint for art. There are exceptions to every rule though. When hanging art over a console, or something similar, keep the art low, so it is incorporated with the furniture.
Photo Credits: hgtv, http://www.dreambookdesign.com/2012/09/design-inspiration-monday_10.html, http://www.drivenbydecor.com/2014/10/gallery-wall-how-to-design-tips.html, potterybarn, http://www.highfashionhome.com/room-ideas/living-room/roman-peace.html, http://www.housetweaking.com/2013/07/11/his-hers-nightstands/, http://jennywolfinteriors.com/residential/#!/hamptons-cottage