The 'Wall Street' star, 69, recently reconciled with the Welsh beauty after working through their personal troubles, which emerged following his 2010 tongue cancer battle and Zeta-Jones' subsequent treatment for bipolar disorder, reported Contactmusic.
They made their return to the red carpet as a couple at an event in April, and now Douglas is sharing the lessons he's learned over the years.
"Marriage requires constant nurturing... You can never take your marriage for granted. It goes to the idea of where you spend your energy and attention: Do you spend it with strangers, trying to show everybody how nice you are? Or do you cherish your partner and really don't worry about other people...