I would like to speak about 2 things:
1) Perspective. Sometime your perspective is correct, some time it is off. I think the reason is that you know how to put box, cyclinder and spheres in perspective. But you do not know how to use them to draw more complicated objects. The trick is to simplfiy what you see and to try to describe everything in terms of basic forms. For example a head can be seen as a sphere (skull) and a box (jaw). Once those basic forms are put down and correct you can move on, adding more basic forms to create more details. You can repeat this process how many times you want. But take care one step should be correct before moving on. So always check what you did. I guess that this process is called construction, at least it is how I would name it.