Some really excellent replies & QTs: Rural areas- use those highway mile markers and exits! Look for water towers and radio/cell towers too. Urban- cross streets & transit stops! Suburban- cross streets, shopping centers, neighborhood signs!
EMS tip for bystanders: The first thing dispatch is going to ask for is a location. If you don’t know the exact address look for landmarks, businesses and street signs. Hell, the bus stop & route number can work.