Thumbnails they are called. It is important to sketch [on any scale] small drawings as research compositions before you start a new drawing or painting. Use your favorite graphite pencil or charcoal. The main objective is to figure out composition and what works the best in your artwork. First figure out what the main focus will be; what do you want the viewers to see as the subject. Remember how color will affect main focus as well as lighting. Then taking into consideration the light source. Each thumbnail is meant to be different; change the light source, move the main subject within the small sketch to see how the composition changes by moving the objects within the small sketches. You may find you like for example the main subject matter not in the middle but the left side. Very importantly not to copy someone’s artwork. You may look at photographs of the subject matter but do not copy. Copying destroys the integrity of your artwork; plus you are not learning at a pace you could be advancing. The artist you are looking at has figured it all out for you. The reward comes from the honest beginning.
Remember line direction, movement with line within the composition; the way your eye follows line and how it moves throughout the piece. The gesture of lines and how they are hard or soft flowing lines or gesture lines.
Here are a few sketches Tom is working on for insight to his next painting. 
