Some of the key diagrams that candidates worry about are the free body diagrams. Many candidates have been kept up at night trying to understand the assumptions and working out the angles.
It's important as mentioned previously to demonstrate not only that you can draw the diagram but also that you can orientate the person you are explaining to. Tell them “this is the force in Newtons..this is the distance in metres..and this is the Fulcrum/centre of rotation”.
A free body diagram discussion is incomplete if the assumptions are not mentioned. There are certain facts that need to be understood.