Town design tips

Just to not make any more new threads about this... but, when you design your town just do it randomly or based on some criteria?

At the beggining I was just putting stuffs everywhere and expanding lands such a crazy and desorganized person, but few days ago I started to redesign the whole town and if you have the chance to visit me you'll see (at least what I tried) to make a part of the town residential, other part industrial, other part commercial and so on and on.

How do you do it?