The easiest option is probably this letter generator from the Student Press Law Center.
You can find our recommended template here: WikiFOIA suggested template.
This is from the Wisconsin Freedom of Information Council's website:WFOIC template
All of these are really pretty similar, but by looking them over, you should be able to get an idea of the language and style that is standard for many requests. You will also get a good feel for what information you really ought not go without when writing a request, e.g. your contact info, a citation of the law, the date(s) of the records you are requesting, etc.