Some ideas to try out to see if they help:
* Add more plot complications and conflict.
* Give wordage to a character's reaction after something happens. So if character finds a body on the floor, then follow it up with a reaction to finding it.
* Do something with the minor walk-on characters. If a waitress makes an appearance in the story, see if you can come up with something else to do with her later on the story.
* Don't forget the subplots.
A book that might be worth reading is The Marshall Plan for Novel Writing. You might be able to find it at the library instead of buying it. The author, who is an agent, offers a step-by-step guide to writing a novel. While his method of outlining isn't for everyone, there's a lot of goodness in the book that you can walk away with.