This looks great! I personally think it's a very good starting point (if you're trying to get close to that reference render); in addition to what's already been advised, just some things I'd (personally) look into:
Be mindful of your framing. Much of the 'flat-ness' that you're observing is due to that. Notice how the reference render has a much narrower frame and, therefore, pretty much all of the frame is filled by the girl? In your render, there's too much 'dead space' around the subject, space where nothing is really happening.
If you don't want to go with a narrow frame, use lighting to liven-up that wall a bit. Something like, sunlight coming in from the window and stretching out on the wall (this way, you'll establish: the time of the day, and the positioning of the sun in this render, and subsequently, the 'mood' of the render). That'll give the wall some 'personality', and is better than say, putting some posters on the wall, as those will meet the same fate due to the DOF being applied to them.
Keep in mind that taking a good, 'artistic' picture in a dark room with harsh fluorescent lights is difficult, even in real life. You can do it, it'll just be more difficult to establish a specific mood that you might have in mind.
And lastly, quickly in terms of the expression, don't worry if you can't get too close to that reference render as I'm pretty sure that one has been modified a little bit by hand in ZBrush or something similar.
Hope this helps a little!