Begin with time and place. Knowing the year and geographic location isn't good enough. What season is it? What city? A story that takes place in the Bronx in summer will be very different from one that takes place in Anchorage in the winter, even if the plot is much the same. A story that takes place during a Presidential election should include campaign ads and political debates.
Ask yourself what's going on in that time and place. People do more than one thing at a time and your characters should too. Maybe they're falling in love, but they're also commuting to work, buying groceries and washing clothes. How they do these things tells the reader about the world they live in.
Change something. If your readers only want to read about settings they're familiar with, they'll read their own diaries. There are two ways to make a change. The first is to have your characters live different lives from your readers. The second is to imagine how the reader's world might be different. What if the world runs out of oil or the ice caps melt? What if the government falls?
Suggest rather than explain. Work the details of setting into the story a bit at a time. It's not necessary to explain that it's winter when your characters are digging their cars out of the snow.
Include all the senses. What does a cheap hotel room smell like? If you mention the smell, the sound of cicadas outside and the roughness of the bath towels, the reader will have a clearer mental picture of the room than if you used two pages to describe how it looks.
Tailor setting to the length of the story. The shorter the story, the fewer details about setting you should give.