1. Do not follow the example of your predecessors and do not overestimate the power of the UN. It has never really solved anything in this world.
2. Do not follow the example of your predecessors and do not underestimate the power of the UN. Without it, even fewer problems would have been solved in this world.
3. Try to use the power of the countries that are members of the UN to your advantage -- they have more than you do. Go on friendly terms not only with the "world leaders" (I have a hard time telling you who are they anyway), but also with the leaders of smaller countries. Try to make them your friends and then try to make them friends with each other.
4. Read every day a different newspaper from a different country, not only the ones published in your home country or in the USA.
5. Imagine that the UN headquarters are transported from Manhattan every other day via magic into another city in other country. That means your windows look out onto the inner city of Delhi today, the remains of the Berlin wall tomorrow, and the Danube River the day after.

This, I know, is easy to say but tough to realize. You've got a big position, so you should expect a heavy job.

Good luck, and all the best from Budapest,

Miklós Vamos