Avoiding sugary things is definitely the main part of keeping your teeth in great condition as they are.
But as someone who personally LOVES sugary things, I've learned to brush my teeth as soon as I'm done devouring that delicious bag of candy :P

It's mainly the mechanical process of the toothbrush rubbing of the nasty stuff from your teeth that is necessary. Toothpaste is just nice because of the clean scent & feeling it gives your mouth.