A perfect world? There could never be one. It's naturally impossible, but if there were to be one...
I'd love to see no fighting, war, violence, tagging, shoplifting, gang bashing or anything to that extent. People respecting the environment and putting their rubbish in a bin, and not throwing it on the streets. A rainbow weekly would be nice too. A world where more trees are planeted, where there's a treatment for everything so no one has to go through endless pain, like cancer. More wildlife and animals would be great, too.
Edit; forgot about racism. No racism would bring me endless joy, as well. I'm sick of hearing racist comments as I walk down the street.