First, you should make a lot of sketches of your main and supporting characters before making a final draft. Make freehand sketches by focusing on different poses.
These freehand sketches will provide you with some good practice and help you in noting down all important points that you have missed or that need to be corrected. Now you should observe the best parts of these sketches and utilise them in your actual figures.
Now take a wide piece of paper or chart and put your ruler on it. Take a well sharpened pencil and mark ruler lines across this paper in order to keep the figures between these lines to give them a disciplined or balanced appearance.
Make sure you have drawn the lines straight and equally distant from each other from the starting point to the end. Otherwise, the figures will seem longer or shorter because of these imbalanced lines.
Now you should draw a face-forward along with a profile view. Furthermore, a rear view and three-quarter turn will also be quite helpful. You can also do a 6-figure rotation in order to complete it perfectly.
You should also pay attention to making the facial features clear and recognisable. Practice by making some freehand sketches of faces that will make it easy for you in creating these images.
While drawing faces, you need to take care of the character hairstyles, expressions, age factor and all other relevant things. You can also keep a mirror in front of you and observe your own face while drawing on paper as your character model sheet is ready.