[Letter of Intent Help!!]

So, I am starting my first year as a grad student this fall and I am applying to be a graduate student instructor for a physical anthro lab! I need to write a letter of intent, but I am not sure what exactly to highlight. I have teaching experience as a docent at a natural science museum and have taken a plethora of upper level/grad courses in physical anthropology during my undergrad career. How should I talk about the courses, and what else could I talk about? Would it be appropriate to discuss personal characteristics (outgoing, enthusiastic, organized, etc), or is it unnecessary/unprofessional? I would love to hear any feedback! Thanks