Hammer a stake into the ground at each end of the fence line. Tie string around one stake, pull it taught and tie it around the other stake. Measure along the sting line and hammer a stake into the ground every 8 feet to mark the location for the posts.
Dig the post holes with a post-hole digger. Make each hole 2 feet deep and 10 to 12 inches in diameter. Pour the cement mix into a wheelbarrow, add water and mix the cement according to the instructions on the bag. Each hole should hold half of an 80-pound bag of cement.
Put a post into the center of the first hole. Ask an assistant to hold the post while you shovel the cement into the hole. Pack the cement with a scrap piece of lumber to eliminate any air pockets. Check the post for plumb with a carpenter's level. Repeat the process and set all the posts. Allow the posts to cure, undisturbed for 24 hours.
Attach three U-shaped metal post fence brackets to each post with 1-inch sheet metal screws and a drill. Place the bottom bracket 8 inches up from the ground, one 8 inches down from the top and one evenly spaced between the two.
Attach three treated, 2-by-4 lumber rails to each bracket on one post and to the corresponding brackets on the next post with 1 3/4-inch deck screws. Repeat the process and attach all the rails between all the posts.
Attach treated fence pickets to each rail with 1 3/4-inch deck screws. Leave a 1-inch gap between the bottom of the pickets and the ground to keep the bottoms from rotting and to help with drainage. Check for plumb after every three or four have been attached.
Pack some of the excavated dirt around the base of each post for a clean look. Finish by attaching a metal post cap to each post.