I have attached a pdf for download which takes you through the key stages to building a SOP and some of the key areas to focus on.
SOPs are used to standardise processes so that everyone has the chance to deliver what the customers want, when they want it and to the required quality level all the time every time.
It does this by helping reduce individual variability and errors.
To understand the benefits of a SOP implementation you can use analysis tools such as Quartile Analysis, Quality Metrics and Basic Productivity Measures.
These four books form the foundation for any Lean / Sigma practitioner at any level the first two are aimed at the application of technical skills covering everything from basic affinity diagrams, VSM's to correlation analysis and so on. The other two books focus more on stakeholder engagement and team working, which are a must if you are leading the change.
Just click on a picture it will take you to amazon so you can have a better look.