Learn to draw from memory
There are two sorts of creating. One is when you draw an object or subject which you can see, which is in front of you. This is called model drawing. Then, the other type of drawing is to draw from your own memory. This particular technique requires tons of experience. Because it’s a good thing that you actually see what you want to draw inside your head. But you will need to remember all details with punctuality and you have to have a huge expertise behind your back especially about anatomy and light effects, for you to be able to draw something out of memory.
Once you drew a tree a hundred times, it won’t be a problem for you to draw it from memory. But if you have never drawn a tree before, then it will not help that you can picture the tree in your head, without the exact knowledge how exactly to draw a tree and its branches and leaves. Therefore exercise tons, to be able to draw things /persons/ any subjects out of memory in the future.