Measure the distance between posts on your deck and write down the measurements. Make sure you measure flush against each post each time to ensure you achieve a tight-fitting railing.
Cut your bottom and top stock rail pieces to length using a power miter box.
Cut your baluster pieces to lengths of 20 inches each. The simplest way to do this is to set up a stop block next to your table saw so that you can just set the wood on the guide and cut it to the correct length each time.
Line up your balusters along the bottom rail and screw each baluster into place. Position the balusters 6 inches apart along the entire rail.
Set the top baluster into place and nail it securely with two nails.
Set the rail into position between the posts, making sure that both ends are set in place at the same time.
Screw the rail into the posts using finish screws at a diagonal angle.
Paint the wood with exterior wood protector paint, in a color of your choice, and allow to dry.