The art of tuning is finding and removing constraints. In most systems, performance is limited by a single constraint. However, removing that constraint, while improving performance, inevitably reveals a different constraint, and you often have to remove a series of constraints. Because tuning generally involves decreasing the load on one resource at the expense of increasing the load on a different resource, relieving one constraint always creates another. A system will always be constrained.
When you choose to remove a constraint, consider which resources can accept an additional load in the system without themselves becoming worse constraints. Tuning usually involves a variety of actions that can be taken, each with its own trade-off.