If you’re painting a scene set in the future, it helps to consider the period of time leading up to it. Some of the vehicles and buildings might be brand new, but others might be holdovers from an earlier period in your world’s history. Surviving elements from earlier times might show wear and tear, or they might reveal changes in the culture or even the government of your imaginary universe.
Here’s one of the concept sketches for Fritz, a “hoverhead” robot that I designed for Dinotopia: First Flight (1999). First Flight is actually a high-tech dystopia, set in Dinotopia's distant past, with vehicles based on the design of dinosaurs. Fritz is based on a ceratopsian head. He's rusty and dented, an outmoded model, and he’s missing the chrome ring that’s supposed to go around his right eye.
Early science fiction paintings, TV shows, and movies often showed a world where everything was in neat, new condition and was designed in the same style. But in real life we’re surrounded not only by the latest technology but also by antiques and out-of-date equipment that we keep using. Adding this sensibility to your science fiction artwork can give much more believability.
Here’s a plein air sketch in pencil and markers of a Buick Special. Note the rust stains, the cracked window, and the fender that has been replaced with a different colored panel.
You can give your future a “lived-in” look by adding such signs of decay: rust, dents, skid marks, pot holes, chipped paint, broken glass, dead bugs, bent corners, peeling labels, faded lettering, graffiti, litter, trash, and weeds. In both digital and painted artwork, surfaces usually come out looking pristine and new, so adding these qualities takes deliberate effort.