Provide a detailed description.
If you can consistently reproduce the problem with specific steps, submit those steps. Even if you don’t know the exact steps to consistently reproduce the problem, try to provide as much detail as you can about what you were doing when the problem occurred: What operation were you performing when the problem occurred? What type of document were you using? Did you recently use any plug-ins? If the problem is specific to a particular file, feel free to share the file via Dropbox or some other file sharing service and include a link to the file in the problem description.