I think that a big part of any novel is the story world that it's set in. Often, it can either make or break a novel. I'm currently working on an untitled young adult fantasy novel that I hope to have published within the next three to five years and writing the story world is one of the most interesting and difficult things about it. Not just the story world, but the different settings that I want my characters to visit (within reason, of course).
One thing that I've gotten into doing is looking at pictures for inspiration. For me, this is a really effective way of getting into the feel of the scene that I'm planning to write. In the novel that I'm writing now, I know that there's going to be a scene where my MC and the LI (love interest) come across a gypsy camp, and spend the night in a caravan. (I feel really uncomfortable referring to him as the love interest because he's much more than that. But for now, we'll leave it at that.) I need to be able to describe the way the gypsy's lantern casts shadows of dim light across the wall, the way the room smells of spices and mint leaves. I need to explain the way pale moonlight trickles in through the windows, edging our love interest's face in silver.
Creating atmospheres is extremely important when writing a scene. You cannot fail to explain what the character is smelling and feeling and tasting and seeingbecause if you do, you're leaving the reader in the dark. And reader's do not like being left in the dark, take my word for it. There are also going to be a few scenes in my novel where our characters are travelling through the forest at night, their bodies drenched in pale moonlight. I need to be able to make the reader believe that they are in a forest, rather than sitting warm beneath a mountain of bed sheets while the static of their television hums quietly in the background. And how am I going to do this? That's simple: by practicing.