For six sigma:

The first step on ensuring quality is to “Define” or gain understanding of the process by separating the process into its basic components so that they are easily understood (Input & Output). The use of flowcharts are common for this step.

The second step is to establish a measurement system that is reliable for the process so that you could “Measure” the current performance to detect problems (if any) and hence could also measure changes for improvement made to it.

The third step is to “Analyze” the process performance by using statistical techniques such as SPC, DOE, etc and hence pinpointing areas where improvement could be made. This is where most of the real meat of the work is done.

The fourth step is to perform the necessary “Improve”ment based on your understanding of the process and also the insight given by the statistical analyzes made on step three above.

The fifth and last step, are establishing “Control” procedure to ensure that any improvement made will be maintained and not lost. Things like SOP are normally used for this purpose.

Obviously, in the past, there has been other quality initiative in place and the tools used in six sigma (statistics, graphs, etc) are also not new but six sigma really accumulate all those available tools and provide the well defined roadmap needed so that you could attack any process in a systematic way and accomplish your goal.

Hope this helps.