I'm putting together a new campaign/setting, set in the late-20th-century U.S., based in a region with which I'm a bit personally familiar.

I've never done a near-present real-world campaign before and I wanted to see if anybody experienced in doing so has any general advice, time-savers, resources, etc. that they feel like sharing. Stuff you wish you'd known at the beginning, maybe.

If it matters, the campaign style is paranormal/cosmic horror and the system we're going with is GURPS 4e. My GMing experiences for the last 10+ years have been in D&D and d6.