What I find helpful is drawing stick figures first. When Im happy with the pose and the proportions, I add mass to the sticks. Just be aware that a stick figure should have a triangle for a pelvis and an extra line for shoulders.
Let me give you an example:
Lets say I want a gladiator. He is in the middle of the fight, in a stable position, his knees bent, holding a small shield and a gladius.
A quick doodle resulted in this:
His arms are too long, his shoulders too wide. a quick edit later I have this:
Ok he is leaning a bit too far forward, he seems like falling over:
Ok thats just wrong. It looks like his back is broken. I need to move his feet forward a bit. In this step I added a little volume to be able to gague the mass better.
His legs are too short, and his upper body too long. His arms are too short again.
This looks quiet good, so lets clear him up a bit, so we can see where he is still lacking:
This is still far from really good, but its a start. We can go back a step and continue from there, or we can try fixing the outline.
There are a few points I wanted to show. Firstly, and this is very important, find a pose. The pose of your char is not very realistic. His left arm bends outward, wich is a very awkward position to hold a lance. Also, the angle of the lance seems off. Dont draw things there ust because there is more space, that will result in such poses. Secondly, you can do the doodles with multiple lines. The advantage is that if the correct line is in the bunch of lines somewhere, the brain filters it out. Thirdly, dont be afraid to use the tools you got. If you need longer legs, stretch them with the stretch tool. If your char bends forard, use the rotation tool to get him lean back a bit. With practice, you will be able to do these transformations by hand, but for learning and doodling, they do the job.
