If you don't smell anything, but you still think you might have a problem, ask someone you trust to take a whiff. This removes the tiny bits of rotting, stinking food that are probably lodged on and around your teeth. You also need to brush your tongue - neglecting the area where most bacteria hide can leave you with nasty smelling breath. Brush your tongue from the back to the front. Do this with a little bit of toothpaste or with your brush dipped in mouthwash.
Antibacterial mouthwash can help defeat the odor forming bacteria.
These little hand held aides have become very popular recently. Use them twice a day when you brush. Tongue scrapers basically scrape the bacteria off your tongue, helping you to have fresh breath. Going to the dentist twice a year should be a part of your routine, and if you haven't gone in a while, it's time to go. Have your teeth examined and cleaned while you're there.