Those white canvas tennies looked pretty sharp before you went out to play frisbee in the park. Now they're covered in mud, grass stains and whatever strange substances you may have stepped in. Don't despair: Canvas shoes are almost as easy to clean as they are to get dirty.
Consider running the shoes through your washing machine. Although many shoe manufacturers discourage this practice, I personally have had very good results with it.
Remove the "easy" dirt. Bang the shoes together outside or against a wall to remove caked-on mud. Scrub the surface with a damp cloth until you can't get any more dirt off.
Take out the laces and any non-canvas inserts.
Rinse out the shoes. Rub the sides together to help get out some of the dirt.
Mix water with mild detergent. Dip an old toothbrush or some other kind of bristle brush into the detergent, then scrub the shoe with it. After you get the stain out, rinse the shoes again.
Wash the laces with a load of whites.