Measure the width of the gift box that you have. Since you have to cover two sides, multiply this measurement by two. Allocate two inches for cutting and overlapping. Cut the wrapping paper according to dimensions of the gift.
Spread out the wrapping paper on a fat surface like a table with the fancy side facing downward. Place the gift box on it right in the center.
You will have two small sides open. Fold them in a way that they make triangles. So now you have two triangles sticking out on each side. Bring up the triangles from both sides so that they meet at the center of the box. Tape them there. You now have a perfectly packed box.
Put the ribbon on the table and place the box in the middle of it. Bring it from both sides of the box to the center top. Twist it there and tie a knot. Now make a bow out of it. Some ribbons come with pre-made bows which make your work easier.