Swish one tbsp of oil such as olive oil in your mouth for 10-20 minutes. Spit out all the oil and rinse well with cold water.

Any bit helps, but the longer the better. Some people do this before brushing their teeth in the morn as they shower, some do it as they check emails or bathe. Dont do it while moving, you dont want to swallow the oil as its getting out impurities.