My son plays with his toys or draws and paints but never clears the mess. How do I make him learn that he needs to clear the mess that he makes?

Every time your child is done with his drawing tell him that he needs to clean the mess and you will help him. Tell him that not clearing the mess is not a good habit. Ask him to sit with a cloth and mop to clear out the mess. Remind him to keep his things in place.