What is best natural way to get soft and smooth stools when constipated?

Yes you do: One with constipation needs to be sure there is no other disease causing it. If constipation is just due to slow movement of the food and poop through the gut, then the things to try are vegetables, water, prune juice, prunes, fiber plus water, Miralax (polyethylene glycol), Senokot or other senna, milk of magnesia, other laxatives, etc. A doctor can evaluate and may prescribe a drug like Linzess.