Although some writers have problems writing too many words for their novel, other writers find when they finish their first draft, they have too few words. Here’s some ways too increase your word count without making your story boring.
Flesh out any areas where you’re telling about a scene and not showing it. Every writer can find at least a few places where they’re doing that.
Develop layers of subplots. Subplots will make your novel more interesting. One word of caution – make sure your subplots connect in some way with the main story. You don’t want a bunch of bunny trails.
Develop minor characters. Spend some time turning your one dimensional characters into interesting people. Here’s a link to help you create interesting characters.
Don’t allow talking heads. Talking heads are stories where two characters are talking to each other on an empty stage. There’s no description of where they are or what they’re doing. If you find this in your story, give your characters bodies and a place to stand while they’re delivering their dialogue.
Add description. Too much description can slow down a story, but adding descriptions, especially descriptions that affect the characters in some way, will make your story richer.
Add interior monologue. Get inside your point of view character’s head from time to time. Let the reader know what she’s thinking.
Blow something up. There’s nothing like blowing up a character’s plans and goals to increase the word count of a story and to make it more exciting. Here’s a link that tells more about this.