How would you use your knowledge in a pre-modern society?

As modern humans we have a whole ton of knowledge that our ancestors didn't, but making use of it seems largely to require the infrastructure of modern life as well. If, via time travel or an apocalyptic scenario, you found yourself in a pre-modern society with no technology but your knowledge intact, how would you put it to use? Of what practical value would common scientific or technological knowledge be? Your goals may be to accelerate human development, make yourself dictator, impress people or anything else.