So my father told me stories about growing up in far northern Wisconsin and I wrote that novel from his descriptions. When I got here, there was little that I didn't already know. The only thing I added to the novel was the look of the eastern white pine trees. Nothing prepares you for those spreading arms if you are from the West. Two thoughts here: Listen when people tell you stories. You not only learn about them, but you will know things beyond your own experience. These pieces of truth you can tuck into your own stories like calico into a quilt. Second, pay attention to details. The small things about a place make a story sing. If I have someone walking on Grant Avenue in San Francisco, I should know the view they will see, or the smells they will smell, or the difference between Grant and Stockton Street. At least if I want to impress a San Franciscan - and if I write about their town I should. For a great YA read that takes place in San Francisco read Cory Doctorow's Little Brother.
Now, think about how you would get that kind of detail if you haven't been to a place. There are ways to do it. And for an exercize, try this. Think of a spot you know well - your backyard or the block your school is on, maybe a favorite camping place or your grandmother's kitchen. Write down everything you remember about it. Are they mostly things you see? What do you hear? Smell? Touch? Now pick a sound or smell from that place and write about how it makes you feel. This is the beginning of giving your story a sense of place. It may even give you an idea for your writing.