Richard Robinson shares his techniques for drawing, especially for drawing everything in proportion. Normally, if we do not have proportion in the picture it would not be complete and fine. The proportion gives the picture more real feel, more dimension and more depth. Technically, you should draw a horizontal line with a dot. Afterwards, you should draw a person below the line. Next, if you want another person, you should measure how big it should be. You should draw two lines to the head and the feet of the first person. Then, with those lines, you will have the dimension of the other person.
Richard Robinson Studio Guides you in Drawing
See the amazing tutorial below and try to replicate its image.