Before you get started you want to make sure and do Market Research. Market research is done for two primary reasons. One is to gather information about a product or industry including information on who your competitors are. The second reason is to identify where to market your product or service. The resources needed for these two purposes are very different.
You will be answering the questions: Does my product exist? and Will it sell?
We have put together a Market Research Guide to help you through the process.
Another thing you will want to think about is licensing. Will you produce and sell the product yourself or license it to a company to produce it?
Resources
The Inventor's Bible by 
How to License Your Million Dollar Idea by 
Turning Your Great Idea into a Great Success by
Once you have created and tested your prototype you will want to look into protecting your intellectual property. This can involve registering for a patent, buying a trademark or copyrighting your work.
Resources
United States Patent and Trademark Office - Rocky Mountain Regional Office
1961 Stout St, Denver, CO 80294
(303) 297-4600
Patent, Copyright and Trademark by 
How to Register Your Own Trademark by