First, you should ensure that you brush your teeth often mostly, three times a day after every meal. The most crucial part when you're brushing your teeth is, to ensure that you thoroughly brush your tongue. It usually holds most of the food particles.
Normally the odor you are smelling is because of a decaying tooth or teeth. You should make an appointment to visit your dentist and have them repaired. This will stop a lot of the odor you are smelling.
To keep your teeth from smelling you can try the following: