The Northeast Document Conservation Center (NEDCC) has some great free resources about object conservation. They recently came out with a primer on digital preservation as well. From their site (http://www.nedcc.org/),
click on 'free resources' on the far right.
I'm not a preservation/conservation specialist, but (generally speaking) the colder and dryer and darker your storage area, the better off you'll be. For specifics on temperature and relative humidity, I would look particularly at the NEDCC's guidance for audio recordings and/or video as a baseline for magnetic media.