There are many way. It all depends on what is your application and hence, what quality of thin film is okay for that particular application. If you don't about film having cracks, then chemical bath deposition or other crude methods can quickly do the job. If you want still better quality you can prepare by chemical evaporation. For best quality thin films, you can opt for pulsed laser deposition or sputtering. If you can specify your application, I can answer more specifically.