As the Warrant Officer Recruiting website states...your letters should be personal. They should not be general....in other words if I take your name off the top and replace it with mine, if the letter is still true...then its too general. Make sure the letters include things that you have done personally and have the officer or whomever tie that into your character as a person.
Don't be afraid to ask the officers in your chain of command. (but use the chain of command in order to speak to them)
Hope this helps.