Marketing question for the self-employed

I'm a recent self-employed IT consultant and would like to hear how others like me continue to receive income after a successful server network deployment. Do you offer maintenance contracts? The reason I ask is because I'm finding myself doing successful projects, but I keep needing to find many more projects to keep consistent income flowing. I believe I'm missing a marketing opportunity with the clients I currently have. What are some other ways others generate consistent income besides network install projects?

Thank you.