Veteran actor Michael Douglas has vowed never to take his marriage with Catherine Zeta-Jones for granted again after their brief separation last summer (13) forced him to re-evaluate his life priorities.

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.

They made their return to the red carpet as a couple at a New York event in April (14), and now Douglas is sharing the lessons he's learned over the years with readers of America's People magazine.

Opening up about life and love, Douglas states, "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...?

"Like a lovely orchid, or anything else that's nurtured, marriage prospers and grows, but if it's ignored, it withers."

The actor goes on to advise any parents struggling with marriage problems to be honest with their children, because "they know everything".

Douglas, whose eldest son Cameron is serving prison time for drug charges, also encourages mums and dads to take immediate action if they suspect their kids are battling drug problems.

He adds, "After they turn 18, you have no control anymore. However difficult it might be, if it looks to be a real issue, then you almost have to go for overkill."

Among the other life lessons, Douglas shares in the pages of People, he stresses the importance of treasuring "the time you have with your parents", adding, "Enjoy them while you can. You never want to look back and say, 'I wish I'd...'"

Douglas is the son of acting legend Kirk Douglas.