Don't get ripped off
There are a number of companies and individuals out there that wish to turn your enthusiasm for your invention idea into money in their pockets, regardless of how good your idea actually is. They'll almost always tell you your idea is great, has incredible potential, and basically make you think you've won the lottery. That may be true, but don't let your enthusiasm cloud your better judgment.
These entities are famous for suing anyone who tells people about them, so I'm not going to name names on this site. Suffice it to say, you should read the US PTO's "Scam Prevention" page and the information about "Invention Promotion Firms" at the FTC's website.
You should also join a local non-profit inventors group, such as Inventors Forum, which I co-founded in 1990. Such groups exist to help educate inventors on how to profit from their inventions, and typically host a seminar series that's open to the public, and private meetings where inventions are evaluated in confidence. To find a group in your area, go to the United Inventors Association website or search on "inventor" or "inventing" at MeetUp.com.
So you've conducted a quick patent search and a quick market search, and still think there's nothing like your invention out there? Here's what to do next.