Any good backyard design includes plans for privacy, and the easiest privacy structure to build is a lattice screen. Lattice blocks the view but is open enough to keep you from feeling closed in. You can grow vines on it and it fits into almost every landscape. You can construct a lattice screen as a deck railing or as a fence in the yard.
As a deck railing, attach posts to the deck either with through posts at the corners and taller rail posts in between, or tall rail posts throughout. You'll need to dig postholes and set posts for a detached lattice fence. Just make sure the fence line is square to the landscape feature of your choice. If its function is to provide privacy to the deck, it should be square to the deck, no matter how far away it is.
Lattice is prone to warping, so buy the thicker 3/4-inch stock and support sections 6 feet long and longer with vertical battens fastened at half the width of the bay (the space between posts). Lattice frames look better in smaller 4- to 6-foot bays.
Expect to spend about 3 hours installing each 6-foot bay. Before you begin, lay out and set footings for a fence. Also make sure you're comfortable with the needed skills for this project: measuring, cutting, fastening, and digging.