To build a wood fence, place stakes to mark the corners of the fence, and connect them using a string. Place stakes every 8 feet along the string to mark the locations for middle posts, and dig out holes in those places. Fill the holes with some gravel, insert the posts in them, and fill the holes with concrete. Add a mason's line to the posts, attach support boards to them, and attach the privacy boards in place.
When placing a string between corner stakes, make sure that it makes up an angle of 90 degrees at each corner stake. You can place middle posts less than 8 feet apart; the general rule is to divide the distance between two corners by eight or less, as you need to have equal distances between the middle posts. When digging the holes, make sure that their depth is a little more than 1/3 of the length of the posts you're planning to insert in them. The holes need to be wide enough to have space left after the posts are inserted.
Use a post leveler to position the middle posts in the holes. Fill each hole about 2/3 of the way with instant concrete, fill the rest of the space with water, and stir the mixture. Once the concrete is set, fill the rest of the space in the holes with dirt. To add a mason's line, connect the posts with a builder's line at the same height above the ground. Nail support boards to the posts spacing them no more than 24 inches apart.