I would do several things.
One, narrow the gap between wealthy and poor. Make more of the world "Middle Class" like it used to be decades ago, instead of this complete discrepancy between the very well to do, and the poor.
Two, give people who are kind to others, good things, and make the evil people suffer.
Three, find cures for diseases of suffering like Cancer, AIDS, etc. (I'd say this even if my mom didn't die of cancer).
Four,make the world safer.. both from things like terrorism, and crime. My mom used to talk about how, when she lived in the Bronx as a little girl, their family would leave their doors and windows wide open, and the only thing that might wander in is a stray cat. If one did that in today';s world, they would be robbed, assaulted, or killed.
I'm sure I could think of others, but those are some of the main things.