I was wondering what are the ways that one can protect itself legally when it comes down to a system which allows file uploads and sharing, is it enough to write a "content policy"?
Do I need to actively enforce deletion of copy-right'd files?
Is there some sort of a pre-written content policy which I can use?
You will not only need a very strong policy against it, but you will have to be ruthless in your enforcement. DCMA notice compliance will be key to staving off litigation, and is really the only way you can remain in operation. If you get a notice, you need to serve it ASAP, and make sure you handle your users in a way that means there is zero tolerance for copyright violations. Even through all this, you are still legally liable for any data stored on your servers. If the RIAA, or MPAA really want to get you, they will.