Below Are Proportion Guides from the book Figure Drawing for All its Worth by Andrew Loomis, published c1920. (A great book if you can get your hands on a copy!) Use them to help you with your proportions. It is recommended that you print them and stick them into your sketchbook for reference.
For some additional help here are a few Youtube videos on the subject of BASIC HUMAN PROPORTION. If you encounter a good one, PLEASE share it with the class!