Degreaser, a brush, and some good, old fashioned elbow grease.
Depending on what material your shoes are made out of, that foaming shoe cleaner might be effective.
Or, you could just be like me and simply not care how ratty your shoes get.
Try a bit of rubbing alcohol on a cloth. You'll need to re-polish the shoe later.
Finger nail polish remover
Depending on what it is. If it is just rubber scuffs, just use your palm and rub it. It may hurt a little because of friction, but it is likely to peel off. What the marks are, basically, is just melted rubber from the shoe. So friction, eg:rubbing your palm into it, will likely melt it again and lift it. Another way is polishing it, to try cut it out.
There is an eraser for suede. It will rough up the nape and the water marks will disappear.
You can try using a Magic Eraser or a clean cloth with some vinegar to gently rub off the scuff marks. You can also use a mixture of baking soda and water to create a paste and scrub the marks off with a soft brush. Additionally, using a white eraser or a toothbrush with some toothpaste can be effective in removing scuff marks from white shoes.
spit in your car
Black is a traditional color for school shoes because it is neutral and versatile, matching easily with school uniforms. Black shoes are also seen as practical and durable, hiding scuff marks and dirt better than lighter colors. Additionally, black shoes are considered formal and appropriate for a school setting.
You take it to a black smith's and get another shoe!
you could use baby oil or go to a pharmasist and they could recomend something.
Black shoes would be suiteable for a white suit
You get a bulldog with permanent black marks that are hard to scrub off?
According to this forum, http://forums.iboats.com/showthread.php?t=295220, Clorox Cleanup is a good solution for black marks on boat seats. The black marks are most likely mildew and will come off easily with Clorox Cleanup without damaging your seats.