What should I do if my mouth smells?

The best way to make sure that you are maintaining good oral hygiene is to visit your dentist regularly.

Brush your teeth two to three minutes at least twice a day to remove plaque and food debris. It’s very important to brush your teeth before going to bed.
Flossing will remove food debris from in between the teeth that a toothbrush can't reach. If the food debris is not removed, the bacteria will begin to feed on it, causing bad breath.
Brush or scrape your tongue to remove any residue that may be building up between the taste buds and folds in the tongue,
Be sure to drink a sufficient amount of water (six to eight 8-ounce glasses) daily to avoid dry mouth. Drinking water will help keep odor under control because it helps wash away food particles and bacteria, the primary cause of bad breath.
If you ever needed another reason to quit, here’s an easy one: smoking contributes to bad breath. Tobacco tends to dry out your mouth and can leave an unpleasant smell that lingers even after brushing your teeth.
Snacks of crispy, fresh fruits and vegetables step up your saliva flow between meals to help wash away bacteria from teeth, tongue and gums that can cause bad breath. These snacks can also help alleviate bad breath caused by hunger or fasting. An empty stomach from skipping meals can cause foul breath as acids in the stomach build up.
If you have chronic bad breath, you should visit your dentist first, to rule out any dental problems. Or, if your dentist believes that the problem is caused from a systemic (internal) source such as an infection, he or she may refer you to your family physician or a specialist to help remedy the cause of the problem.