What's one easy thing that nearly everyone could do in order to simplify their lives?

• don't ever - if at all possible - buy on credit
• consider before buying anything whether you truly need it or only want it; also, what will the maintenance of this thing involve and what will other consequences be when owning it
• learn to be content with having enough; have a healthy view of "enough"
• Have a healthy routine in life (so do not commonly approach days weeks and years with "let's see how things go")
• speak with people who have successfully simplified their life
• try to have realistic expectations

...and so forth.