Bad breath simply comes and goes for some people. Perhaps we only wake up with bad breath in the morning. Or eating certain foods, like onion or pizza. These are more obvious triggers for bad breath. But the bacteria that release the volatile sulfur compounds of bad breath find a great breeding ground in tongues that are coated or lined with cracks. Mucous and phlegm also contain proteins, and these bacteria exist to break down proteins. So if you suffer from phlegmatic nasal conditions, there's a good chance there is an associated increase in bad breath.
However, despite any existing conditions like fissured tongues or excess phlegm, that are more difficult to change, there are things we can avoid to minimize bad breath occurring.
What makes bad breath worse?

• A dry mouth:
  
  Saliva keeps bad breath at bay because it is rich in oxygen. The bacteria that lead to symptoms of bad breath are anaerobic bacteria, meaning they live in an environment that does not have oxygen. When you have a dry mouth you're creating an environment that is more similar to their 'home', one that has little oxygen. So the bacteria thrive, and so does bad breath.
  This is a problem for people who sleep with their mouths open, in particular. Breathing through your mouth all night dries out your mouth so you wake up with less-than-pleasant morning breath.
  
• Certain foods that are high in protein like meat, and for those who are lactose intolerant, dairy:
  
  If you don't digest dairy products well, the bacteria have more of a chance to digest the proteins in milk and produce the volatile sulfur compounds that result in bad breath.
  
• Not flossing:
  
  Similarly, if you don't floss after a meal, especially if you've eaten meat, the bacteria in your mouth have ample time to break down the meat proteins stuck between your teeth.
  
• Acidic foods and drinks like coffee:
  
  Acidic foods and drinks create an environment in which bacteria will multiply faster
  
• Alcohol:
  
  Even if its in a mouthwash, alcohol will dry your mouth out, and then you have all the bad breath problems associated with a dry mouth
  
• Sugar:
  
  Sugar is food for bacteria. Enough said!! And this is why even mint flavored sugar products won't make your breath smell any better.
  
• Toothpaste containing SLS, or sodium laureth sulfate:
  
  SLS is a harsh chemical that damages the lining of the mouth, albeit on a microscopic level. In the lab, SLS is used to destabilize membranes, and make protein and fats soluble. That's why it has a 'soapy' or foaming effect. Because it is a soap, it has a drying effect in your mouth. This of course leads to bad breath. It has also been linked to canker sores, and many people who suffer from these have found relief by switching to a toothpaste that doesn't contain SLS.

References:
1. www.therabreath.com