We recommend that you do market research. Conducting a market research will help you and will add so much value to your business. Understanding the vertical and getting important information, knowing where to get all the necessary information is the best way to learn your niche. Check the market in certain locations to know where to target and where to start.
You may start by using google.com to search for services in specific areas, you may call and email the companies too so you can talk to them and ask questions.
Just to give an idea, of the 10,000 plus niches there are easily 5,000-25,000 of each... just Google How many plumber business in USA.., for example... keep in mind all you need is 10 or if you are a go getter 50.