Depending on your climate you may want to cover your deck to make it more comfortable. In rainy areas like Seattle it might be wise to build a roof over one section of the deck. In hot and sunny areas like Phoenix it would be preferable to build a shade canopy or pergola. Screening in the area may be useful in areas with lots of insects. Covering your deck will add to the labor and costs of the project but may be well worth it if it allows you to enjoy your deck for more days throughout the year.
Another option is to install a water drainage system to allow you to use the space under your deck. Some people install screen walls under the deck as well to complete the enclosure. This allows an alternative outdoor option for less ideal weather.