Use a standard letter-size sheet of paper
Fold the paper lengthwise in half
Unfold it and crease sharply
Fold the top two corners toward the center line
Fold the new top edges toward the center line again
Fold the plane in half along the center crease
Fold the wings down evenly on both sides
Keep the wings straight and symmetrical
Make small adjustments to the wing tips if needed
Launch with a smooth, level throw
Test and refold for better balance if necessary