First, inventors must know that USPTO (United States Patent and Trademark Office) www.uspto.gov provides a lot of valuable help and advice to inventors and a lot of information on how to patent your idea can be found on USPTO web site. During the process PTO examiners can be contacted for advice on the process and application status inquiries.
In 1995 in an effort to make it easier and safer for independent inventors to market their inventions USPTO has created a process of Provisional Patent Application. Such application is somewhat easier to create and file without necessity to use expensive services of a patent attorney and application fees are considerably less than a full patent application. Current filing fee for Provisional Patent Application is US$125. Application can be filed and paid for on-line. It provides "Patent Pending" rights to the applicant and protects the idea for full 12 months. This time can be used by inventor to market his invention to potentially interested corporations and to prepare for submission of a full patent application. Danger of Provisional Patent Application is that if it is not turned into a full patent application within 12 months, inventor looses right to patent his idea, ever.
There are many books and sources, which teach amateur inventors patenting process. One of such invaluable sources of wisdom and legal and procedural information is a book by experienced patent attorney David Pressman "Patent It Yourself" . In his book author gives basic understanding of the patent application process and also describes a great number of PRO advices.
There are many design and engineering companies out there, which can help amateur inventors develop their idea into a viable product and implement it into manufacturing. Just be very cautious of companies which advertise themselves as invention marketing groups, have very impressive names, some have even more impressive TV advertisements. They pretend to be "inventor's best friends" and invite to bring any and all ideas for review. Many of these companies, if not most, are tricksters and they are not marketing or developing anybody ideas. They are only after inventor's money.
One more interesting fact about patenting idea in the USA versus Europe and many other world regions, which inventors must know is that in United States one can have an idea, market it or even manufacture and then apply for a patent for the idea, that gave live to a product. In other words, your idea may become publicly accessible, yet, it ill still be patentable. According to patent laws in Europe, once your idea has been disclosed and known to general public and accessible to such, it is no longer privileged confidential information and is no longer patentable.