Get Your Posts Ready
Purchase specialized fence connectors (see Resources below for a link). Plan on having three per pole to support three horizontal support pieces for each fence section.
Measure and mark the spacing for your horizontal support pieces. You want one in the direct center of your fence, one near the bottom, and one near the top. The top and bottom support pieces do not have to be at the extreme ends but within 6 to 8 inches is a good idea.
Slide three connectors over each metal post.
Use the horizontal tightening screw on the fence connector to tighten each connector over the marked spot for the horizontal support piece.
Install Your Supports
Use 2x4s cut into the length of your fence sections for your horizontal supports.
Have a friend or two with you to hold the support pieces in place.
Use a power drill with a screwdriver bit to install two screws through the holes on one side of the fence connector and into the horizontal support piece.
Repeat the procedure on the other end of the horizontal support piece and its corresponding fence post.
Repeat with the remaining two support pieces for that section of fence, then repeat the entire procedure for the remaining fence sections.
Install Your Planks
Measure each fence section and use that measurement and the width of the wooden planks you will use as your vertical pieces to determine how many planks you need per fence section. Since you are building a privacy fence, you should keep them less than 1 inch apart in spacing.
Cut the wooden planks to the appropriate height to match the height of your metal posts. Leave a 1- to 2-inch gap at the bottom of the wooden planks.
Hold one wooden plank next to one metal post so that the plank is on the outward facing side of the fence, and the horizontal support piece is on the inside of the fence.
Use a power drill with a screwdriver bit to install two or three screws through the wooden plank and into the top horizontal support piece, then do the same for the center and bottom support pieces.