Assuming I appear naked in a field in England in 1375, I would first try to, in no particular order (at first, then a particular order)

• find cloth to cover my face and hands so I don’t transmit or catch any diseases
• distill water so I can drink it without getting diseases
• use yams or horse urine to create HRT
• communicate with the locals and seek a local blacksmith to create a metal tube with metal balls inside it, and mix charcoal, potash, and sulfur to make a primitive gun to defend myself against the people who think I’m a witch or a demon or whatever
• talk to the women and encourage them to rise up against the system and patriarchy, teach them how to make weapons, about 4 field crop rotation if they don’t already know it, otherwise about automated steam engines, weavers, hydroelectric dams, etc
• march up to the feudal lord and demand democracy, with the fear of the gun and half the population behind me they will agree
• teach about the scientific method to get them to question things, do their own research, and learn more
• there will be scientific labs, primitive computers can be developed, we can spread our advanced culture to the rest of Afro-Eurasia, also prevent slavery
• warn people about going to America and Australia unprepared, go with them in modern ships and don’t spread disease, talk to the locals and trade with them and learn from them, don’t kill them or replace them. Teach them the tech advancements too
• Write down lots of things, invent the printing press if not already invented, document human knowledge and encourage more documentation by others

This is all if I have any measure of success at the first things and don’t die or kill myself