The obvious thing to do is add some shade. Awnings, deck sails, and covered pergolas make great additions to decks and patio. Awnings are especially convenient as many can be retracted to allow full sun. Deck sails are another great option that are easy to install/remove, and can even be angled depending on the path of the sun over your space. Of course, there’s also always the humble umbrella that’s inexpensive, movable, and easy to store.
Overhead fans are another great way to keep heat on the deck from becoming too oppressive. These take more planning to install and use unless you have a screened in or covered porch, but they can be integrated into open air decks as well. These keep the breeze flowing around you and your guests and make the heat more tolerable. Plus, the added airflow has a tendency to help keep insects away from the space.
You thought hot tubs were only for cool nights and seasons? If you’re hot tub has a good range of temperature control, you can use it to beat the heat too. Either turn the heating unit off, or keep the temperature at its lowest setting, and you can comfortably sit and enjoy your deck, cocktail in hand. Plus, unlike a pool, hot tubs require far less upkeep, and you may not need a fenced in area around it, but be sure to check your local codes and homeowners insurance. This is one addition that truly makes a deck usable year round.