I'll list one of the six now, I've written about it before:
I'd set up a commission to design a global political structure that stably establishes a distributed system of power in the world.
The history of mankind is largely towards a concentration of power. While it's going on, there are always harmful conflits, whether it's between the US and the USSR, or between two local warlords in Afghanistan. As long as it's going on, there will be huge over-expenditure on the military by nations, and therefore overuse of the military hurting people not for the phony reasons given in propaganda but simply for the pursuit of power and greed. People will be treated as pawns and exploited as so many always have been.
Worse, once the concentratin of power finally achieves some global power - say, an alliance of the powerful in all the most powerful region, like a global EU - we can expect nothing other than an indefinite tyranny, where the things that have always helped manking escape tyranny are no longer feasible. There won't be any US to counter tyranny in the USSR. There won't be any dependance on one key leader like Alexander the Great, the system will not be threatened. There will be no real recourse, and the governing power may well likely determine that all that 'freedom of information' that leads people not to like the government too much is counter-productive, and they'll ensure everyone is given the information to be a nice cattle. What's anyone going to do about it? It's not as if tyranny tends to fall from internal pressure, especially when it's the only game in town and uses modern governing techniques for population control. All that military force and technology will have only one target, the citizens.
No, what we need is neither conflict nor centralized power, we need a stable political system which keeps power distrributed to many powers around the world, none dominant and none needing or allowed or able to try to pursue the conquest of others. It's that or tyrrany, probably.
England never decided to divest itself of the colonies; it would have happily ruled the world, just as any power would happily do so. There can't be another military revolution.
That's one of the six, to set up a stable global political system with power distributed(others will be inclined to cooperate because it protects their autonomy).