Look around you. Everything near you now can serve as inspiration for your writing. Even the places most familiar to us can seem new and strange at times. Take 5 or 10 minutes to write down as many details as you can notice in the space around you. Then, grab a mirror, look at the room's reflection, and write about the changed perspective.
Observe new places. Go to unfamiliar places where you might find it easier to observe closely. Try a new theater or a different grocery store. Go to a place that looks empty and simple, then try to write down 20 details of that place. The more you look, the more you will find. Again, take 5 to 10 minutes to write down as much about the place as you can.
Compare your observations with others. Take a friend to a coffee shop or park, then after ten minutes of writing independently, compare your lists. You will begin to notice how different your perspectives can be. This will allow your creative imagination to flourish. You can also try to list details by memory of a place you know well, then compare that list with a sibling or friend over the phone, to see if she remembers the same details.
Read. One of the most helpful things a writer can do is read. Pick up some of your favorite reads or a book you've never read, and pay attention to the descriptive pages. Research which authors are known for their descriptive scenes, and try to imitate their style. Look at some of your lists you made earlier and try to write out a scene with those details in the style of your chosen author. For some examples, see John Steinbeck's "The Grapes of Wrath," Herman Melville's "Moby-Dick" or Cormac McCarthy's "The Road." Notice also how different these authors approach their descriptive scenes. Make note of how their execution and purposes differ.
Write. Take time every day to write a descriptive scene. You may find it useful to do without characters or plot in order to get descriptive. Maybe imagine a photo in your mind and describe it top to bottom, left to right, or center to borders. Alternatively, remember a place or person from your childhood (just a place or person, not an event) and try to describe it to a friend vividly. Try to re-create the feeling the image gives you by choosing your words carefully. Or try to describe the scene giving it the opposite feeling; this will make you pay attention to the details as well.