Depends on rivers and mountains and stuff. If you have a small town on the Plains with no real rivers or anything, I think it would naturally be somewhat squarish, and you'd probably have about 20 streets by 20 avenues in a grid, with one Main Street, and possibly a Main Square park in the middle of Main Street surrounded by major shops.
Another thing is if the town was designed in modern times to move cars and stuff, or if it grew organically from a watering hole, and was designed to move, at most, a horse through an alley.
I live in mountainous region now, and most small towns here have a main street, no square, and they are built up in the valleys, but not up the sides of hills (they could fall down in landslides). A lot of times, there will be one main street that forks off into two valleys, and there will be a few side streets running parallel to the main street(s).