***If you have one great book or article in hand, what can you do to find more like it?***
1. Follow citations backward and forward
References are older than the source at hand.
"Citations" or "Citing Sources" or "Cited by" are newer than the source at hand.
2. Click the links for "Related" or "Similar" sources (in Google Scholar and other databases)
3. Follow the author (in databases and/or on social media)
4. Plug the title into MathSciNet, get the primary MSC code, and use that MSC code for more searches.
5. Similarly, look at assigned "Subjects" or "Keywords"; use them for more searches.