That is actually a difficult question. Living simply means different things to different people. As I have tried to practice it over the years my concept has evolved, and will probably continue to evolve as my priorities change. At the moment I believe that living simply means getting rid of the excess in our lives in favor of the basics, and getting rid of those things that do not positively contribute to our lives in favor of those things that fulfill us. Things can mean objects, projects, jobs, or even people.
One of the ways I have simplified is by becoming a SAHM. I decided that my kid's care was more important to me than my job or the income that it brought in. Now that my kids are getting older, and will be able to start preschool soon I may decide to go back to work or work more extensively from home.
Another way in which I have simplified is by getting rid of nearly everything in my home that had no greater purpose than collecting dust. Now my house is rather more empty than it was, but those things that remain have value for me and my family. In getting rid of those things I have saved my self time and money on the upkeep of those objects that I can instead spend on something that really matters.
Does living simply mean getting back to basics or living like the Amish? It can, but I think that "basic" living simply highlights those aspects of our lives that matter. It highlights family, people, self reliance, and social connections; however, a technologically advanced lifestyle can highlight those values as well.