Considering that this would be an alternate timeline and have no effect whatsoever on the one I currently inhabit, I would go the selfish route and just load a car with as many almanacs, newspapers, computer printouts, and other materiels that relate to all the major events of the past five years and seek myself out in late 1999 where I will strike up a partnership, allow him to do all the legwork to guarantee our massive wealth by gambling, expert stock market playing, and winning at least one of the mega jackpots in some state lottery, and then do my best to prevent any tragedies that I can, such as stopping the murder of one of my friends in early 2000 and hiring someone to seek out and murder the 9/11 hijackers in summer 2001.
According to Huntington’s “The clash of civilizations”, the primary source of conflicts in the years to come will be cultural divisions, in particular between the western Mithraist world and the eastern Zoroastrian world, involved in a 2000 years old struggle for supremacy…
In other news the famous telehighpriest P.J. Falbertson stated yesterday that the decay of moral values…
I would go back to Rwanda and ensure that the Canadian peacekeepers on the ground had the support they required to keep 800,000 people from being murdered.
That, plus I would ensure I had the right lottery numbers for that time period, as well as archived stock market reports (for purely selfish reasons, of course! :))
It’s been a while since I read A Connecticut Yankee in King Arthur’s Court, but I recall that the time traveller had all kinds of problems from Merlin when he was thought to be a competing wizard (I think I’m right on this).
Anyway, most of my time travel schemes involve going back and introducing the concepts of basic sanitation and sterile instruments to the medical community of the day. Sounds boring, but how much needless misery did mankind suffer until viruses and germs were understood? Everyone would be better off - fewer deaths from diseases and infections, cures and operations would be much more successful and I would become a rich doctor to boot.
Back to the Connecticut Yankee, where my plan breaks down is when my powers to heal are seen by others as supernatural instead of scientific. Either I’m seen as a threat to other courtiers’ influence on the King when my skills work, or I’m exposed as a “fraud” when I’m told to heal something beyond my abilities like a crushed skull. In the end, I end up dead, exiled or in the dungeon.
What if I tried to introduce agriculture reforms to increase food production, or introduce electricity? I don’t thinks it matters, some individual or ruling body would see my ideas as a threat and eliminate me eventually. Pessimistic I know, but just look how much flak Copernicus caught just for saying the Earth revolves around the Sun - and he was right!
My back up plan would be to take guitar lessons for two years then go back 60 years or so and become the greatest rock and roll star EVER. Then I wonder if younger people would get tired/envious of my ability to stay on the charts for decade after decade and decide to make anything-but-me the new hip thing, just to rebel.
To be honest I just wish I could go back three days and avoid catching the flu.
To clarify, I’d become the greatest rock and roll star by performing all of today’s classics before the original stars were discovered. I’d need two years to get the basic chords and melodies down to memory. It’s low I know, but it’s my time travel day dream and if you don’t like it get your own. 
Interesting that you’d go to the Council of Nicea instead of Judea a few hundred years earlier. 
Just imagine being there for whatever happened, and getting to write an actual eye-witness gospel–imagine the utter shock of archeologists when, 2000 years later, they discover an carbon-dating authenticated ancient scroll called “The Gospel of Ted” written in modern English.
For those of you that would want to do the lottery and prediction thing more then once, after you have already done it history will never be the same. So, after you play one ticket and win, history will be completely and irreversably changed, possibly meaning you won’t be able to do this again. Got to take into consideration this.
Who needs to win more than once? Not me - I would be happy with one big, say, 20 million payout, and invest in stocks I know will do well
Wouldn’t it be easier just to find out what Booth did that day before going to the theater, meeting up with him, and perhaps cutting his throat in a dark alley somewhere?
Or maybe just shoot him with a supressed pistol in an out of the way spot?
How about taking a video camera back to 33AD and making a documentary about Jesus and his followers?
Then seal the tapes into some very secure container and hide it where you know nobody will find it for 2000 years. Or maybe just in the Dead Sea Scroll Cave.
Don’t bet on it. The same kinds of people who did those things on your list would have found some other excuse to do the exact same things.
I’d just go leave a laptop on Edison’s work bench then go for a walk. I doubt he could make heads or tails of it but being in his posession rather than some random guy on the street will insure it isn’t thrown into a fire or something like that. Should screw up the future quite nicely.