The first thing you should do is to get your teeth professionally cleaned by periodontist or a dental hygienist. After that take care of your oral hygiene as poor oral hygiene is the prime factor responsible for diseases of gums and bad odor.
Before brushing, floss each and every tooth properly. Then using a soft bristles tooth brush, clean your teeth for at least 5 minutes. After that use mouthwash to do gargles.
After every meal, rinse your mouth with water and maintain a proper oral hygiene. For more info on oral hygiene visit the link....http://www.identalhub.com/articlecategory-dental-health-98.aspx