Do you watch any bottle diggers on YouTube? That rapidly accelerated my knowledge of all things dump digging, along with perusing this and other bottle sites.
Do you have a cemetery dating back to the 1800's in your town? Does that cemetery have woods next to it, and better yet, a creek running through it? That's one of my go to spots if I have a limited amount of time in an unfamiliar city. Your mileage may vary.
If you check out some YouTubers, I recommend Digger Dave Beeler, Southern Searcher, and Adventure Archaeology. Just between the three they probably have a combined century of knowledge and they freely share a lot of it with viewers.
Is there a local bottle book for your area? Seek it out, study it. Chances are it'll be hard to find, out of print, and a little pricey, like the one I have for my area. Probably still a worthwhile purchase though, along with other books you can get your hands on.
Do you have a probe? Do you know any local collectors who might show you a long picked over dump they swear was dug out in the 60's? I don't believe in dug out in the 60's. There's still millions of bottles in the ground. You'll find some nice honey holes. Good luck!
See if there are any old atlases from your state that would have old properties listed. PA has a site that has aerial photos from the 30s-present that i use to compare to the old maps as well
I've actually came across 2 seperate dumps while geocaching, you may consider trying it. It brings you to those random areas that you wouldn't otherwise go to!