if you're doing a modern town start with the roads and the layout you want it to be.
Do you want it to be crowded with houses right next to each other, or something more quiet like a little town with few houses near by?
Okay so, start with the roads. Determine how busy everything will be. After you make the roads start with some buildings, i recommend you try making a downtown like area with restaurants and little shops, then expand and make the shops less and less until you get to the houses.
That's what i'd do. lol.
Like what Aplem said:
I usually start with getting some inspiration from real life.