Step Three

Tajima PZB-400 Plumb Bob
Now the posts will begin setting and you can proceed to cut the 2 x 4′s into twelve 8-foot lengths. These horizontal fence rails will be the support for the pickets. Measure 12 inches from the base of the posts for the lower rail and 36 inches for the top rail with your measuring tape. Now make a mark on the back of the posts at 90 degrees. Using two 3-inch galvanized steel drive screws, attach the rails.The marks will serve as the top edge of the rails, with each rail butting against the next one on the back of each post. The fence rails attach to the outer posts, which are cut to attach flush with the edge of the post.
Step Four
You have the option to use prefabricated fencing sections, depending on how much work you are wanting to put into this fence, and how talented you are at woodwork. Lay out the pickets with 2 to 3 inches in between, use a 3-inch-wide level as a spacer, if your creative you can even make your own spacer jig. On the ground below the rail lay a leveled 2 x 4, this will be a base for keeping a consistent height of 2 inches from the ground. Use your nail gun as you evenly space the pickets, attaching them to the rail.
Step Five

Empire Level 6820 Measuring Tape
You will now cap the fence posts with finials, on each and every post, measure exactly one inch up with a measuring tape such as the Empire Level 6820, then attach the decorative finial with finishing nails.
Now you have a brand new picket fence to provide some security, and to makes your property look complete. Painting and finishing the fence is an open ended option, depending on what the desired overall look of your property is.
Sources:
http://www.diynetwork.com/how-to/how-to-install-a-picket-fence/page-2.html#step1



