[header] How to make a sanding block [title] Select a wood block. [step] You can use a small block of off-cut wood retrieved from the scrap pile, provided it's the right shape. A rectangle is the optimal shape because it's easy to hold and covers a good area when sanding. 
If needed, cut a piece of ordinary wood into a rectangle of a size suitable to hold in your hand (around 2 " x 4 "). [title] Fold the piece of sandpaper over the sanding block.