As a futurist, editor and writer Kevin Kelly’s published works have included “Out of Control,” “What Technology Wants,” and “The Inevitable,” in which he speculates on future trends and technologies from a largely optimistic point of view. (His bonafides also include founding “Wired” magazine and advising Steven Spielberg on the movie “Minority Report.”) But another one of Kelly’s books came about almost by accident. On his 68th birthday, Kelly began recording the things he’d learned throughout his life with the intention of passing them on to his children. He found he had more to say than he initially thought, and his list of advice eventually grew into his book “Excellent Advice for Living.” Among the compendium of wonderful, heartfelt guidance is this recommendation to balance work with relaxation, which reminds us that resting well is just as key for productivity as hard work.