I do a lot of drawings and I can't echo the above. It's a great start, but you have a long way to go.
Firstly it's great to see that the proportions are solid. This is one of the things most people that even attempt to draw struggle with, and it really underpins the realism of a drawing.
Your main problems lie in the tone of the pieces. You have solid outlines and neutral shades of dull grey which doesn't look realistic at all. Pencil is really not a good medium for drawing realistically. It's great for blending to create smooth, light surfaces (like skin) but try and experiment with charcoal to create vivid blacks where there is shadow. Merging the two has great effects. Look up J D Hillberry for an idea.
If you are using photographs as a source, change them to grayscale and up the contrast and the brightness to gauge an idea of how your drawing could look.
Keep at it. Drawing is a wonderful hobby and you are off to a good start.
I hope my comment is more helpful than those above.
