Reviewing some anatomy right now and I thought I would share this with everyone here. Maybe it will help some of you as well!
I knew where the triceps originate and insert, but I didn't know how to draw it when the other muscles are included as well. Maybe I didn't watch the lessons closely enough, but I couldn't find that information anywhere. So I just googled it haha.
I've learned that the long head of the triceps will go above the Teres Major and then go under the Teres Minor and the Infraspinatus. Keeping this in mind, you will be able to correctly insert the arm into the body when drawing the back view.
If there is something wrong with this, please point it out to me!