PDCA Cycle:

The plan–do–check–act cycle (Figure 1) is a four-step model for carrying out change. Just as a circle has no end, the PDCA cycle should be repeated again and again for continuous improvement. It is also called PDCA, plan–do–study–act (PDSA) cycle, Deming cycle, and Shewhart cycle.
Figure 1: Plan-do-check-act cycle

PLAN
Establish the objectives and processes necessary to deliver results in accordance with the specifications.
DO
Implement the processes.
CHECK
Monitor and evaluate the processes and results against objectives and Specifications and report the outcome.
ACT
Apply actions to the outcome for necessary improvement. This means reviewing all steps (Plan, Do, Check, Act) and modifying the process to improve it before its next implementation.
It can be used
As a model for continuous improvement.
When starting a new improvement project.
When developing a new or improved design of a process, product or service.
When defining a repetitive work process.
When planning data collection and analysis in order to verify and prioritize problems or root causes.
When implementing any change.