Keeping things simple takes:
saying no to over scheduling
saying no to materialism
playing a bit daily for balance
exercising routinely for health
creatively expressing myself daily
being dilligent with the resources that are available
living withing the our means
no comparing to how others are living
I ask myself constantly this question when tackling things daily "Does this fit in my life and life's goals?" If it doesn't then I don't allow it to take my most valuable resource- time. When I have to force schedules to mesh and go through multiple mental yoga moves to get something done, it means it is too complicated and doesn't really fit into the time/resources I have at that moment and I pass on it if possible.
Above all simple living is taking time to share a smile with family and friends, to see the beauty of nature around you and having moments to tell yourself how wonderful things are.