If setting is particularly important or unusual, it can play a key plot role, e.g. post-apocalytic or alternate history stories. This is common in (wo)man versus nature and (wo)man versus society stories.
It is important to be clear and specific with your settings. It's through setting that authors build their world. Make your world as unique and fascinating as possible! Authors never want readers to be confused--because that takes the reader out of the story. Don't give readers any extra excuse to put down your book. An unclear setting often gets comments like "Set the scene" from critique partners. I must admit, I've gotten my fair share of those. :)
Readers need to know where geographically and temporally the characters are at the beginning of each new scene. They also need to know which characters are in the scene.
Closely related to settings are descriptions... Usually, you must use some kind of description to give your setting. Interestingly, literary fiction tends to use many more similes and metaphors in its descriptions than genre fiction does. Recall, a simile is when something is "like" or "as" something else, and a metaphor is when something is described via analogy.
So, if you want to "lit-up" your genre fiction, consider adding more similes and metaphors.
In recent years, I've noticed physical descriptions of characters are rarely given any more; definitely do NOT describe your character with a laundry list of characteristics, e.g. brown hair, brown eyes, brown skin. If you do describe your characters, make sure to do it in the context of the point-of-view character, e.g. 'her chocolate skin made him want to lick her all over.' :)
Generally, laundry list descriptions of anything are the mark of a beginning writer. Don't do it!
Good luck with your settings and descriptions.