When I was writing a cover letter for a volunteer position, I found some volunteer cover letter samples online.
These were very helpful and gave me a guideline to follow. Since this was the first time I had done a volunteer cover letter, I didn't know quite how it should be worded.
I think it is important to highlight your skills and experiences without going into too much detail. You want your letter to paint a good picture of yourself without someone feeling like they are reading a book.