What grant program are you specifically writing a grant for, R01, F30, R33, etc.?
Anyways, this quick start guide from the NIH is probably a good overview of how a grant application should be laid out:
http://deainfo.nci.nih.gov/extra/extdocs/gntapp.htm.
My own advice is when writing any type of grant, you better know your science and the literature that pertains to it. The worst thing about writing and submitting a grant is to have it come back, post-review, saying that it's already been done or the proposed science is not solid enough.