What kind of preparation does a patent application require?

As you noted, the easier you make it for the patent attorney, the easier it is for the attorney to prepare a good patent application. Other than in a chemical application, which normally does not have drawings, you will need to put together a written description of your system, apparatus, or method constituting your invention. In addition, you will need drawings showing what the system or apparatus comprises. Try to provide as much as possible to the attorney - the attorney will then review it and probably discuss it further with you in order to ensure that the final application is complete, accurate, and thorough.