The Power of Less
The Power of Less - Leo Babauta
At almost 10-years old now, The Power of Less set the stage for many of the books we see today that are about the magic of tidying up or life-changing impact simplifying has. It's a very simple and straight-forward read, which is why I think it's so great. There's a little bit of everything in it to help you accomplish more by not spreading yourself to thin.
From organizing your tasks, saying no to commitments, setting goals, getting in shape, and staying motivated - this book covers it all in simple terms and to the point.