Please suggest what to do for constipation related problem.?

I suffer from constipation related problem for which I have not found any satisfying cure. To be precise, the problem is hardness of stool, (NOT lack of regular bowel clearing) which sometimes give rise to painful anal fissure. I take lots of vegetables and even Psyllium seed husks (known as isabgol in India, one teaspoonful in half glass of water) every night before going to bed. I go for walk for forty minutes every day. What else should I do to take care of my problem? I am afraid this may in long term give rise to complications like colon cancer. Thanks for suggestions.