Measure the width of your front door, then measure the height of the door using a tape measure.
Stage the three pieces of lumber on the floor, making a "Z" shape. Then draw diagonal cut lines on the middle piece of lumber using a square and pencil.
Put on eye protection and cut two pieces of lumber to fit the width of the door using a circular saw, then cut the middle piece to create angles at both ends with a miter saw.
Arrange the three pieces of lumber on the floor again in a "Z" shape to ensure the angles match up properly.
Fasten the top piece of lumber to the front door horizontally using stainless steel screws and a screw gun, then fasten the bottom piece of lumber to the front door with more stainless steel screws.
Fit the middle piece of lumber between the two horizontal pieces. Fasten the middle piece to the front door using stainless steel screws and a screw gun.
Paint the front door lumber brace with matching paint using a paintbrush to finish the job.