not sure why most people are blindly praising it when it obviously has issues which you could hint upon how to improve.
first things first, the cap looks bad and I see what you were trying to do with it, but, in the end it looks like hitler gelled his hair because of the poor use of brushstrokes. next time make the strokes more even so it fits the shape of the hat and so that some sort of depth is there.
the background is shit, I think you know how to improve on that.
the eyes are okay I guess, you need to use reference to see the proportions and the details etc, but, I quite like what you did with the pupils.
the upper lip of the mouth needs to be smaller, again, look at a reference for generic proportions.
eyebrows are simple, but well done.
I like the way you tackled the nose, although as bloom highlighted above, the nostrils are a wee bit large, but the way you switched between line size and gaps gave it a sense of contrast even if its slight.
yeah so if you start art, you're not going to pull perfect ideas out of your ass, especially when in comes to portraits, so use reference before you draw with your imagination.