Place the paper (printed-side down) on the table with the folded edge toward you. Put the gift on the folded edge, leaving enough paper on one side to cover the end of the box and add 1/2 inch. Do not move the box.
Estimate the same amount for the other end, as shown, and make a pencil mark where you want to cut. Fold the paper at the pencil mark and cut on the fold (or cut according to the gridlines, if the paper has them).