Reduce air friction or "drag" by making all surfaces as smooth as possible. A blunt, rounded nose causes less drag than a sharp nose. A good design has all leading edges rounded and trailing edges tapered to reduce the drag.
Rubber bands should be lubricated before the race. They are the "motor" and must be strong and flexible.
Use a sharp knife for cutting the grooves for the hanger fitting and fins. A dull knife will crush and splinter the balsa wood.
When you start to carve, remember that the end with the small hose is the rocket nose.
A potato peeler is good for carving the shape.
To help increase the rocket's speed reduce the wall thickness to a minimum of 1/8 inch. Do not weaken the area around the hanger (carrier) or carve away the nose button circle.
Do not apply too much paint to the outside unless you sand between each coat.
Be careful not to get glue on the plastic carrier, especially in the holes through which the monofilament line runs. Glue can interfere with smooth operation.
Make the propeller shaft as short as possible by bending it close to the prop. Cut off the excess wire with wire cutters.
Test the rocket's balance by hanging it from a string through the hole of the hanger fitting. If the rocket is nose-heavy, carve or sand a little wood off of the end. It it's tail-heavy, remove wood from the tail area.