I might as well give some advice now that I've been summoned (thanks @jensrichard77 <3).
Before starting I usually take some basics in account for the initial layout:
1) How big the is the city? Is it a capital city? A village? This is just to get a basic size.
2) What's the terrain like? If it's in a rocky/irregular place the layout might be more chaotic as it tries to adapt to the diferent slopes. Also consider water as well, if there's a river nearby the city will probably expand along the riberbanks rather than getting away from them (same with portuary cities).
3) How's the civilization that built it like? Real Life examples, imperial roman cities had a very neat layout with straight streets while other cultures went for more narrow streets and cluttered houses. Also do they have city walls or not?
Once I take all of that in account I start making a quick sketch of the terrain (rivers, cliffs, forests...) around the city and plan accordingly. I take a broad brush and start blocking random shapes that may fit an actual building layout while leaving the whites in between as the streets or city squares. Once it's all done I start putting labels on them following how I think a real city would work. Usually shops will be around the main streets and squares. Hostals will be near the edges of the city since that's where their patrons will set foot first. More shady business will stay away from the crowdy places as well, and so on.
At least that's how I like to do it, I hope it could be of some help!