I write letters on an almost daily basis. Last week I wrote 4. I think that Ursa's suggestion is appropriate. Make sure that you and head coach are on the same page and I'm sure that the head coach won't mind. In fact, I think it is good that you too are writing letters. I address things like work ethic, attitude, commitment, academics, ... I have 3 "styles" of letters that I write. I am ALWAYS honest about what I am going to say to a player. I let them and their family read it before I send it out. Finally, when and if you ever feel the need to say no, say it! You'll only hurt your school's program by being kind to someone that might not deserve a letter of recommendation.
Granny said Sonny stick to your guns if you believe in something no matter what. Because it's better to be hated for who you are than to be loved for who you're not.