I'd suggest starting by building yourself a basic ISMS framework (Information Security Management System)and bolting IT policies on to it.
I've spent just over 13 months doing exactly the same job as you've just been given (long, hard slog, no shortcuts) Once you have the basic high level IT/IS policy in place, use others as bolt-ons, i.e. Internet access/usage policy, Email policy, System specific policies, Equipment/usage policy, Mobile Policy, Remote Access Policy, Safe/Secure disposal policy, DR/BC, Server Policy, Update Policy, AV Policy etc.
Watch your back, though - you need to get these passed by your HR and Legal sections so current statute can be included. Bear in mind the level of knowledge/common sense of the average user - don't write it in tech-speak, write in clear English!
Google BS7799 or ISO 27001 (versions of the same thing) and you'll get some good pointers.
Good luck - as I said, 13 months in, and still going!
GG