Captain Kirk was always demanding more out of his Chief Engineer on Star Trek by saying, “Scotty, we need more power.” And his response was always, “But Captain, I’m doing the best I can.” Predictable and fun. But what if you’ve finished your manuscript and 
submitted it to your agent or publisher, and were told you needed more words. You’re under contract to deliver a certain amount of words, and you’ve come up short. What do you do? Do you “pad” the writing—go in and add a lot of stuff just for the sake of word count. Padding usually involves “staging” or additional extraneous actions by your characters as they move around the “stage”. But doing it too much will call attention to the padding and wind up getting sliced out by your editor. Intentional padding is not the answer. But there are some legitimate ways to increase word count without bloating your story.
One suggestion is to build up your story’s “world” by conducting additional research and adding a few bits and pieces of atmosphere throughout. Let’s say your scene takes place in Miami Beach. Your character is having breakfast on the balcony of her hotel room overlooking the Atlantic. Without slowing down the story, add a few lines about the history of the hotel. Since most of the hotels on Miami Beach have been around for decades, certainly something might have happened years ago at the same local that could reflect on or be pertinent to the story’s plot or situation.
Another method is to utilize your character’s five senses. Are you making good use of them? Sitting on that balcony, your MC must be able to smell the fresh sea breeze and hear the gulls calling from overhead. Or she notices the ever-present container ships slipping along the horizon in the Gulf Stream. Could be that she can feel the film of salt coating the arms of her chair. How does her freshly squeezed OJ taste? You don’t want to use all 5 in every scene, but engaging the senses is a great way to expand the prose and take advantage of an opportunity to further develop your character.
The skill in expanding a manuscript is to do so without appearing to pad the writing. And you want to avoid going down a new rabbit hole and suddenly winding up with too many words such as introducing a new subplot. Always consider the two basic criteria for any additional words: they must either advance the plot or further develop the character. Otherwise, they don’t belong.
What about you? Have you ever come up short on contractual word count or just felt your story was too short? How did you expand the story without it becoming blotted or obviously padded?