Do what you know. That is, you should start a business that focuses on what you have experience in. That experience can be either prior work experience or a personal hobby that you're ready to turn into a career. Even if a business idea seems highly profitable in theory, don't start that business unless your heart is in it. While profit is important, it likely won't keep you coming in early every day and driving growth.[1]
For example, imagine you have experience making coffee as a barista or waiter and want to turn your passion for good coffee into a small business. You would already know a good amount about the industry and be able to apply not only your knowledge but your passion to your work.