Hi Twilight,
Very difficult to answer these questions. No doubt you have tried to look up textbooks and found they tell you everything
Some very general prinicples are (and these are loose off the top of my head)
1. Support the fracture - this should be done in a cast usually but sometimes neck of humerus is difficult. Jull in the 80s produced some sort of protocol i think about mobilisation of these fractures.
2. If a muscle crosses the joint, then be careful with activating it strongly - such a general statement i know but this is a general question!
3. The principles of fracture management should be in textbooks - for instance, i just looked up Clinical Sports Medicine by Brukner and Kahn and it had many different fractures listed in the index and management for them. Otherwise, i usually sit there and think up what i want to do and then chat to someone about my ideas to make sure i am not off my head!
Perhaps some case studies??