Dress up your deck by adding a pergola. The pillars support a lattice where woody vines may be trained. The climbing plants provide some protection from the harsh glare of the sun. For a low-maintenance feature, instead of a lattice with plants, you may choose to put canvas to give shade. You can also install gauzy curtains around for more privacy.
(Photo from sallywheatinteriors.com)
If you have a second-level deck, make use of the area under it to have more outdoor living space. You may choose to decorate it in the same theme as the second-level deck for continuity or embellish it in an entirely different scheme for a different atmosphere.