By preparing your grant narrative ahead of time, you allow for others to proofread your draft prior to submitting your application. Since you won't be able to make changes later, this is a key step of the process.
Narratives should be clear and concise, thoroughly explaining your departments need and how funding will enhance your department's operations. Avoid pre-formatted grant narrative templates; your firsthand knowledge of your department's operations will enable you to write a more persuasive narrative.
Lastly, always write your grant narrative in the required format.