I think the most good I could do would be to go back to the mid-1700's colonial America, probably a center of education like Philadelphia, Boston, or New York. Patient a couple of simple but yet-to-exist technologies like the addiator calculator, rifled gun barrel, etc, but especially the optical telegraph. I would try to leverage these devices/systems into myself joining the Continental Congress as a representative. The optical telegraph is 100% technology that was possible, but not in existence and one that I think could have had unforseen relevance to the founding of the United States. Imagine if long distance, nearly instantaneous communication had existed when the Constitution was being written... think about the implications of that for communication privacy protection. Might even be able to convince the founders to include such a system to be part of the constitutionally mandated post office. I think all it would take would be to point out how important communications had been in the War of Independence: "imagine Savannah has been attacked by Spain. It would take several days for a place like Boston to be alerted to that event... with the optical telegraph the whole nation would know within a matter of a few hours." After all that, I'd probably try to help get germ theory off the ground and write rebuttals to push back on the various scientific racism theories floating about at that time.