Excuse the quick and sloppy paintover, but hopefully it shows what I'm on about:
Removed the Klingon-looking forehead lines. These aren't necessary and if you are using them to denote age, you should also have lines around the mouth and eyes, showing an older character.
Adjusted shape of face near the eye. Not a major change.
Lowered and thickened eyebrows, made them more realistic shapes.
Removed lines from around eyes. The way you had them before, I could see what you were trying to do but it is better achieved by altering the shape of the eye itself. Also, I tried making the expression he is making and it isn't possible to have your eyebrow up like that while squinting your eye!
Shortened nose at both ends so the bridge doesn't extend upwards as high and the nostril doesn't curl down.
Moved the mouth up. Where you had it before gave him a distinct lack of chin. Where it is now, it works with the shape of the face at the side as you can see where his jaw starts
Moved ear to the right. It should be on the side of his head rather than on his temple. I also added more detail to the ear to make it... err... more ear-like.
Adjusted the neck underneath the ear slightly and the other side of the neck so it looks like a more natural pose.
The pupils of the eyes could stand to be a bit bigger, but I've left them as they were.
Not all of this was strictly necessary. You're on the right path, the key is just to keep practicing.