"Having impurities" is a vague description.. is your skin excessively dry and discolored? or is it on the oily side and you have blemishes that mar the complexion?
I would suggest that you start drinking two cups of green tea a day, with the juice of half a lemon and a teaspoon of honey. Don't use a physical exfoliating agent e.g a scrub if you have acne.
Increase your fluid intake and stay away from coffee and colas.
A multivitamin supplement with zinc takes care of the dullness.
I would be able to suggest more once you have specified the problem your skin is facing.
PS. Avoid taking stress!