hey man, looks like you’re just getting started modeling, and you’re doing a good job so far! Especially with faces, to get good with this stuff is a lot of work. When I was getting started, I modeled around 5 crap faces for 1 that I was satisfied with. This is already a lot better than some of my first models, and you’ve also done a great job adding in the topology!
So the first thing is looking at the overall shape of the face. Here, having a end goal really helps. You should find reference of what you’re trying to do and try to emulate it. Here, I just overlayed a picture I found on google.
This is a picture I found, but you should do this with a picture you’re trying to emulate. When you’re getting started, it’s good to use other people’s art, so you start to learn shape language and stuff from professionals who have been doing this for years. Having reference is how we learn as artists.
Immediately, though, there are some things we can see that would make your model stand out more. Bringing the nose down, and pushing out the curve of the forehead would help. The neck is really far back, bringing that forward would help balance the head overall. These are things we might not notice without having reference.
A tool I like to use to help me visualize is liquidify in photoshop. I think this is called IWarp in Gimp? it lets you push around bits of an image, so you can start to shape things. Here I did it with your model, to try to get it closer to the reference.
And here we can immediately see the second problem. the resolution of the mesh is really low to get the shapes of the face. You can see there is one face between the end of the nose and the lip, which is not enough resolution to capture the shape of the lips and the nose. I think you could easily double your face count (quadruple even in the mouth area). As mentioned above, the subsurf modifier is awesome, but tends to goop things out, instead of make them super awesome. 
hopefully that helps! Good luck!