This is a bow I made at my friend's house once. It only uses 17 pieces and I think it shoots well for its small size.

Step 1: Collect All of the Pieces

First off let's get neat and organized and collect all of the pieces. You will need what is on the picture below. Above the pieces is what the finished bow should look like.

Step 2: Making the Middle

This is the part the arrow will shoot through. The hole in the center acts as a guide so the arrow will stay (somewhat) on target. The pictures are a little fuzzy but they still should be understandable.
Make two of what you see in the first picture. Then connect the two with the orange connecter like the the second picture. This connector is what the arrow will shoot through.

Step 3: Supports and String Holders

Every bow needs support so it doesn't blow up in your hand. The rods on each side will prevent the string holders from collapsing on themselves. Once again the pictures are fuzzy but I have a bad camera.

Step 4: Stringing the Bow

Almost to shooting! All you need to do is attach the rubber band to one side and make a figure 8 shape with it.

Step 5: Arrows and Shooting Them

Every bow needs arrows! There are some arrow ideas I have posted. To shoot, you slide the back of the arrow through the center hole and pinch the rubber band intersection so it's right above the end of the arrow. Then pull back and shoot!