Kaizen Priorities by Mike Wroblewski:
Priority 1: Kaizen your bottleneck station first – If you don’t know what is your bottleneck station, find it. There are many ways to find your bottleneck: all the inventory is piled in front of it, people downstream are waiting on it, it has the most overtime, it’s a top maintenance priority, etc.
Another excellent post from Got Boondoggle.