Forgetting to brush and floss every day can lead to bad breath as food particles build up in your mouth and attract bacteria. If you don't get regular dental care, you are more likely to suffer from gum disease, which can also leave behind a bad taste.
To improve the taste in your mouth, brush twice a day and floss daily. Rinse with mouthwash for an extra freshness boost. Cut down on stinky foods like garlic and onions, which can leave behind a lingering taste and smell. If you smoke, quit. Smoking not only gives you stinky breath, but it also yellows your teeth.
If the bad taste doesn't go away, call your doctor. You might have a medical condition that needs to be treated.