this is assuming you end up in a culture that would even value technological advancement.

People value their friends and family not dying, and the murdering raiders from neighbouring tribes being kept at bay. And people that don't value that don't tend to last very long.

You’d need the social skills to demonstrate technological improvements (say, a better axe) without causing everyone to freak out and call you a demon.

....Starting with an axe would be nice. The lumberfolk would appreciate it, surely. But then what happens when the old blacksmith blames your witchcraft for the crops failing next year, or for the village chief's child falling ill? So maybe teach the blacksmiths too, so they also benefit from you— I'm sure they'll love having some upstart come in and tell them how to do their jobs.

You're an outsider, no matter what, and you're never going to completely look like them or sound like them or act like them— Can we really think that any amount of social skills will be enough to keep you safe, when they might just be determined to hate you for what you are?

Maybe start with a combination of military and medical technology. Show them a crude crossbow; when they see the next raid of Goths or Aztecs or Mongols or Vikings or Peloponnesians or whomever being repelled before they even reach the gates, they'll come to appreciate it sooner or later… Their enemies are against their gods, so if you helped defend them from their enemies, you must be sent by their gods. Disgustingly, hating the same out-group is a great way to keep yourself safe in any given in-group, whether at work or at war. Medicine's probably trickier, because if you fail to save somebody then some people will probably blame you for their death. But if you make it clear that you can't stop fate from running its course, and you start with some basic stuff, they'll probably come to appreciate that their friends aren't dying as much from infections anymore too.

Fear of death has always been sadly the strongest motivator for embracing technological change. Modern aviation, computing, and nuclear science all came after WWII; and "anti-vax" movements only thrive in countries that have already essentially eradicated the concerned diseases. It'll be harder for them to crucify somebody whom they can see is standing between them and death.