When you brush your teeth before you floss any food, bacteria, and bacteria that are loosened by flossing stay there until the next time that you brush your teeth.  But if you floss first and then brush the particles that are released are removed from your mouth resulting in less dental plaque and a lower chance of getting gum disease.
So remember to floss to loosen food debris and plaque deep between your teeth and brush your teeth to remove the plaque.  If you follow this pattern you'll reduce plaque, help prevent gum disease and don't rinse or put anything in your mouth after brushing your teeth.  This will help you keep the fluoride in your mouth for as long as possible.  You should wait for at least 30 minutes after using mouthwash to eat or drink anything.
To learn some new strategies on how to have healthy gums and have a great oral health routine check out Harvard Health's at-home health care guide.