You can write anything you want here, but i'm pretty sure the world can only be a better place if you start being a better person yourself.

Be kind to people, so they will be kind to others
Share what you have, so others will share too
Say something nice to people once in a while, so they do the same to someone else or maybe to you
Treat everyone with respect, as you know you can only get respected by respecting others
And many other examples as above, making yourself a better person is step 1 in making this world a better place to live on.

Thanks again @svosse for another great question.