Things I tell preschoolers every day that I would like to tell grown-ups:
You need to use your words if you want something. I want to help you, but I only can if I know what you need.
Sometimes, you should just walk away if someone keeps causing you problems. Sometimes, you staying around them is part of the problem.
Ask before touching - people and things.
Worry about whether you're following the rules, not about if other people are. If everyone does that, it'll be ok.
The flowers are for everyone, not just you. Please let them grow.
EDIT: If you play with the water, you're going to get wet. If you don't want to get wet, don't play with the water. (They never listen to this one.).