If your story is complete, don't add words just for the sake of it. My editor warned me against meandering descriptions and dialogue and even events if it doesn't contribute to the plot and move it forward - it's wasted paper and ink, wasted time, and has the potential to bore the reader because they'll catch on that it's just a filler, and no one wants to read obvious fillers. If you really need to increase your word count for whatever reason, think of things and ways to flesh out your characters. Additional body language, dialogue, how could you better describe something or an event, etc. But in the end, if it's complete, it's complete. Think of it as cooking a dish - the dish is just right and if you add even a pinch of salt more to it, you'll ruin the whole damn thing. When it's cooked, it's cooked, overcooking it will just make it dry.
