Don't let inertia become the constraint
Whenever you've performed any of the optimizing steps (exploit, subordinate, elevate) stop and observe the effects. If throughput has increased you've done well. If it hasn't, undo your change and try something else.
Whenever you solve your worst problem, your second-worst problem gets a promotion. There is always a bottleneck, there's always room for improvement.
Go back to the start of the process: identify the constraint! Your interventions may have shifted the constraint to another resource, you need to focus on that resource now. And always keep an eye on the The Goal!
Ever-shifting constraints
When you practice the 5 focusing steps you might feel as if you're playing "Whack a Mole": after every intervention, the constraint has moved somewhere else; you're constantly chasing here and there to find the elusive bottleneck. How can you deal with this situation?
- Do you have several resources whose capacity is nearly the same? As soon as you let one of them subordinate to another, the subordinating resource becomes a bottleneck. Only subordinate resources if they clearly have enough spare capacity.
- Is your bottleneck time-dependent? At different stages through a process, different resources might be loaded heavily. E.g. in a "waterfall" process, analysts will be loaded heavily at the start of the project, testers will be loaded heavily at the end of the project. Consider if you can "even the load" by having the resources who are lightly loaded, subordinate to those who are loaded heavier and vice-versa as the load shifts. In this way, subordinating is a dynamic process. In the example, testers could help analysts at the start of the project by devising automated acceptance tests; analysts can help testers at the end of the project by analyzing test results and making tradeoffs about priorities and cost of finding and fixing faults.
- Where do you want the bottleneck to be? Often, you can (re)design your system in such a way that you can choose where to place the bottleneck. Make sure to place the bottleneck somewhere you control.
What if you get stuck? You can't find any more ways to optimize the system?