If you could go back in time, what would you do? Options

[creole]

If you can go back into time (that won't be affected by the space time continuum), what would you change? For better or for worse?

I'd go back into time and prevent things like 9/11.

[Herizon Action]

First I'd make contraception an acceptable religious practice by going back early enough and convincing everyone that the world would do better if not everyone had babies.
Then, I'd prevent the population booms of the 1900-1950s by making condoms and birth control more readily available and easy to make.
Finally, I'd go to 2004, invest in google, and take high school seriously.