How can I cure bad breath?

See your dentist. See your dentist. Have the dentist rule out decay and periodontal disease. Have enhanced hygiene-- brushing at a forty five degree angle between the tooth and the gingiva, flossing correctly, using a tongue scraper and possibly a prescribed rinse. If the etiology is not determined to be dental, a MD consult may be needed.
Determine the cause. Halitosis can be caused by so many different factors, including but not limited to gum disease, cavities, acid reflux, sinus infection, diet, and tonsil stones. Once the cause is determined, a corrective course of treatment can be recommended. See your PCP and dentist.
See a dentist. If your teeth are not the source of this (often due to disease of the gums), a search for the source (sinus infection, esophageal diverticulus, tonsillar disease and other conditions may cause this. Cannot suggest corrective measures until you know what is responsible.
See your dentist. In the majority of cases, the cause of bad breath, or halitosis, is the product of bacteria in the mouth. The proper diagnosis is the key to a successful treatment. See your dentist for Halimeter test, diagnosis and bad breath treatment that depends on its cause. Good luck.