Next to the hands, the feet are one of the most difficult parts of the body to draw. Even when you are drawing them for a cartoon character. The best way to start out is to use triangles. Make sure you include the HEEL of the foot. look at the picture to see what I mean.
Don't worry about drawing the toes right away. Of course, most of the time, your characters will be wearing shoes...or something a long those lines anyway. Here are some technical drawings that might give you an idea of how to draw the feet/shoe.
Notice, in this drawing you can still make out the triangle that was created in the first picture of the foot.
A view of the bottom of the foot/shoe.
Here is a picture of the back of two bare feet. Now, I'm not a huge fan of this drawing, because the heals are not sticking out as much as they should.
This is a great example of a foot while the character is walking or running. Notice, all the little shapes that are used to draw the foot. Once you've drawn your basic triangle (very lightly so that you can erase), you can add the important details that make up the essence of the foot...including the toes, the heel, and the ankle bone.
Here is a great example of the bottom of the foot. This gives you an idea of what the footprint will look like.