Check out leanstack.com. This is the first thing I do before jumping into any business idea.
Firstly you find a business opportunity----or at least a perceived one.
Then you develop a Business Model Canvas for it.(www.businessmodelgeneration.com)
Then you use the Business Model Canvas as a hypothesis and get out and talk to the target market about your ideas. You test your hypothesis.
you might even read some books in this area.
Then you revise your ideas until you are game to start.
Then you put your toe in the water.
You may also find an advisor who can help you through this process
6 months should be fine but it will go fast. And you may need to raise finance which also takes time.