Start with something you really need to know how to do to get buy day to day. Learn the best way to filter or otherwise purify water, keep stored water pure, build a chimney that draws well, get rid of nightsoil without contaminating ground water, grow food crops without depleting the soil. Then so you can stay alive while you pass on the knowledge learn to build a fire, bank a fire to last the night, find eatable plants, dry and otherwise preserve food, butcher game and fish, tan hides, make rope, trow a pot, Fletch an arrow, spin thread, weave, knit, sew.
Then when you know how to feed and clothe yourself you can fool with all the changing the time-line by building a model T in the dark ages stuff. There's no need for a car without roads, and what good is one without oil wells, or gasoline refineries? If your goal is to improve the lives of the people you find yourself plopped among far better to start with smaller things. If your goal is a better future than the one we have today better to start with some social changes, and warnings of the environmental and social problems that go hand in had with development, so you get mechanical looms without slaves picking the cotton and children working 16 hour days in the mill, miners getting killed daily to get coal for the steam engines which pollute the air and water...