Left 4 Dead/The Town

Paths

 * The beginning of the area, just outside of the tower, is a place where the Hunting Rifle is most useful. Two or three players can pick off enemies across the street from the roof with the other player(s) watching your backs.  Doing this greatly reduces the opposition you will initially see.  In addition, once you've had your fill of sniping helpless infected, you can climb back inside the safehouse where you started and swap for your weapon of choice
 * The sandbag wall in the first area is jumpable. Otherwise, you'll need to through the grocery store.
 * In the second block, enter the florist's building. The double-doors lead to a dead end.
 * Just before the safehouse, you need to climb a set of stairs, climb out the window, and walk across a few roofs.

Traps

 * You need to lower a ramp using a forklift. Doing so sets off an oversensitive car alarm, but at least you have a turret to take care of zombies that charge the barricade.