Interesting, I know something of patent law and actually have several issued in my name ( nothing of value to the general public but in the Semi conductor industery) Its very complex. First you would need to do a patent search and see whats out there thats the same or similar. What I always scratched my head over was the fact that an idea does not have to be proven to work, or even to have been actually done. The idea itself can be grounds for a patent. If your idea is something simple, the best plan of action is to have a working model made yourself. Often, when an idea is presented to lets say a large company within the industery you are addressing.. if its a good idea the very first thing they do is to see how they can get in on it with additional ideas of their own, which they in turn will patent.. and leave you out. Its very dog eat dog out in the patent world.
In addition, I have been asking for clarification on 1 item. Lets say you have an idea. You discuss this idea on an internet forum in some detail. I have wondered if the date / time stamp on that post would stand up in court when someone else takes that idea and presents it. Seems much more valid that sending yourself a letter, but I don't actually know the answer.