Who will put you do death for witchcraft, blasphemy and/or simply failing to know the customs and show them proper respect.
Check out L. Sprague De Camp’s “Lest Darkness Fall”
A fun read, well done, and should give some idea of what could happen under the OP’s scenario.
I consider that a perk. It’s just a tiny little thing called the power of RAWK, maaaan.
That thought stopped me in my tracks. 
So maybe I’m thinking too big. I’ll go back and invent the banjo and introduce them to bluegrass. That should mess up the future.
Poul Anderson wrote a story called “The Man Who Came Early” about this idea.
It didn’t end well for him. The man from the future was just too far ahead.
I’m not sure how much it would advance civilization, but I could show them the Heimlich Maneuver.
I went back in time and invented the guitar. When I came back to my own time, Traditional English Melodies now included “Smoke on the Water” and “Stairway to Heaven”.
So I went back and stopped myself from messing with history.
Actually, leeches do have valid use in reducing bruising, and helping blood flow in sutured areas.
Luckily I get my various innoculations updated by the Navy, and they simply lurve passing out smallpox vaccinations [not to mention I got ones for yellow fever, rabies and bubonic plague. I tend to get the recruit package and the overseas package.]
Being a woman, I have to be much much more careful, I would probably try to hook up with a convent and blend in assiduously. I would spend my remaining life doing good works - I could introduce a few recipes, at least my herbal simples would be mostly harmless. I could make fancy soaps scented with various essential oils - I do know how to extract lilac with cold fat extraction. I also understand simple lab processes so I could introduce distillation and make whiskeys and brandies.
[I would much rather go back to Celtic Britain and try to introduce gunpowder, seige engines, good stout walls and tribal alliances that will stand up to Rome. Call it probably 50 years to 100 years pre Rome.]
And if memory serves the first thing he started with was double entry bookkeeping.
Actually, didn’t Mark Twain do it first?
Capt. Kirk did this in “The Paradise Syndrome” and was immediately recognized as a god. Much more realistically, this gets you burned at the stake for witchcraft.
You’d have to be very very careful not to give them any advanced too far beyond what they already know. To have any chance of acceptance, your new knowledge has to come in tiny steps. And it has to be, not only a small step, but at least reasonably consistent with what they already think they know. Forget about atomic theory or germ theory. It will be incomprehensible to them.
Remember the dictum (someone, remind me who said this. Was it Arthur C. Clarke?) “Any sufficiently advanced technology is indistinguishable from magic.” (a.k.a. witchcraft). You don’t want to show them anything sufficiently advanced.
Lord of the Rings has examples of technology that could only be magic in-story but look perfectly common to us – a notable example being those strings of electric-looking Elven lights they used in the forest. (Did they have power generating plants on the Anduin River?)
ETA:
Did you burn yourself at the stake? 
All this “burned at the stake for witchcraft” talk is kind of over the top.
First of all, not every olden civilization did this, not even every European one. Second, it really varied based on the time and place - much like modern moral panics, sometimes there was a spate of witchfindin’ when the crops failed or the plague was in town and obviously it was somebody’s fault, but mostly country folk actually liked their weird people living on the fringes of society, doing such wondrous stuff as delivering babbies, setting broken bones, curing boils and the like.
OK, so many of these weird people cured boils by applying concoctions of piss, cowpat, amanita muscaria, skin of that toad wot makes you all spacey when you lick it and a pinch of mint for colour ; and then they got stoned when the guy keeled over instantly, but still :). In many places, witchery ? Well respected medical profession for po’ folk who can’t afford the ones that bleed you dry. As well, Catholic monks and erudites would routinely practice rudimentary science and alchemy, even dabbling with the heretick Practifes of the Musselmen - and last I checked Roger Bacon wasn’t burnt, at the stake or otherwise.
People of the past were still, well, people. Ignorant, but not stupid. Getting along to get by, as long as things were going OK.
All that being said, if you’re really paranoid about the torches and pitchfork crowd you could always couch your actual science in the kind of superstitious bullshit in vogue in that place at that time, whether it’s sympathetic magic, the theory of humours, phlogiston or what have you : “Yeah verily, I tell thee the plague is totally caused by vapours arising from the admixture of excrement and fresh well-water - a traveller from Venice told me, who’d heard it from a sage of Cathay so you know it’s legit. Hurry, brother, dig the cesspool over *there *to prevent this unholy curse. And quit dumping carcasses upriver while you’re at it, it’s very bad luck because of… faeries and shit, I 'unno.”
And then he distilled booze, and got involved in a barfight over theology! I loved that scene.
Yep, according to Wikipedia.