Hi,
The most important thing you can work on is learning to
really see. The beginning artist has a tendency to draw from their head, not from their eyes, and as a result, they will draw things as they think they look, rather than how they really look. We draw "symbols" to represent a mouth, an eye, a nose, instead of really looking to see the shapes and values that make up a face.
There are some excellent examples of what I mean in the portrait and reference photo you've shown us. For example, in your drawing, each half of the upper edge of the upper lip curves upwards, like a letter "U". But if you look at the drawing, you'll see that the same cuves actually open
downwards, quite the opposite way. This is a case where your brain decided to draw a symbol for a mouth, rather than looking at the actual mouth and drawing it.
Another example is that the head in the photo is tilted quite strongly to our right: the glasses, mouth, and bottom of the nose all clearly slope down. But there's no hint of this at all in the drawing.
Another: there are very strong lines showing the sides of the nose in the sketch. If you look at the photo -- really look -- do you see any lines at the sides of the nose at all? There are none. Likewise the lips have no outlines in reality, although there's a very dark line between them.
Another: the glasses in the photo are lighter than the surrounding skin; in the drawing, they are very dark. In the photo, the apparent darkness of the eyeglass frames varies; in the drawing, it's constant.
There is
a whole section of lessons on Drawspace dedicated to learning to see: I would recommend that you carefully work your way through all of them.