Cut all identical pieces of wood at once. For example, parallel sides of your drawer will be the exact same size. Rather than trying to make the perfect cuts twice, stack two pieces of wood together, clamp them in place using padded clamps, and cut out the two matching pieces at the same time.
Measure your drawer bottom twice and cut once. Mark the dimensions of your planned bottom onto the wood itself, then measure the distances between the marks to guarantee precision. Cut out the drawer bottom only when you are positive your markings are correct.
Use correctly sized screws or nails when assembling your drawer. If you use fasteners that are too short for the thickness of your lumber, the drawer may not be secure and may move easily. This allows the drawer to shift and warp, and it will not be square.
Check the corners of your completed drawer using a carpenter’s square. This tool will confirm whether or not your drawer is square, since it may be difficult to tell with the naked eye. Make adjustments where necessary to perfect your drawer.