The PDSA or PDCA cycle

This cycle is one of the most fundamental quality improvement tools. 

The 9001 Standard strongly encourages its use.   It is expected to be applied across the range of processes involved in any quality system, from planning for quality and review of performance, through to taking effective action to respond to, and resolve, weaknesses in the system (corrective and preventive action).  

If you use this cycle, practice with it, apply it and use it until it becomes "just what we do around here", you simply cannot fail to improve your quality management system.  And anything else you apply the cycle to.

Plan Do Study Act cycle

First you Plan, then you Do - work the plan.

When you've done that, you study the results and see what happened.  (This stage was called Check, but Deming changed it to Study later, as he found people tended to confuse 'check' with just inspecting).

Act is the last stage.  What you do here depends upon the results of your planning and doing, and what you observed when you studied/reviewed them.  If you got the results you wanted, you build the change into your system.  If you didn't, you decide what else to do; for example, try something else, or start again from a scratch but take a different direction. 

It's a virtuous circle, because the more you use this improvement tool, the better you get at doing it.  

And the more you apply PDSA, the better your system becomes.