Industries change courses, trends, output, labor, technology if you work mainly using the local or regional area you would need to know how important this industry is in the development of your region. Also an industry can be in the incipient form and while still risky to undertake an action it is well rewarding when you keep going on an upward trends that increase the demand for that industry products and services that shape the target markets.
Checking the fundamentals of the industry helps you prepare for short or long term plans and be likely to get results according to your financial forecasts. Industry fundamentals represented by: locations of output production, mobility of labor, changes in technology, changes in production, modifications of the markets, changes in target customers.
Analysis of the industry fundamentals and listening, talking, meeting with experts and key players help you position this existing company that you want to buy from all aspects of the business. Look at the competitors and how many of them were years before, depending on how long this company was in the business and also the number of competitors now, how they evolved: did they shut-down, moved elsewhere, merged or were acquired.
Go to the library, the reference section and get help on how to search about the industry, the key indicators of this industry and others related to it. Librarians help you find also companies in the industry, you can start contact their top people have meetings with them. Also you can simply get in by applying for a job and check it out how you like it. It did not occur to me to do this till I actually got into it, that I could get a job, may not have been paid, even at the company that I intended to buy. Also, I learned on a course, later about that approach: "take a job at the company in that industry" and learn about their environment, relationships. If you are currently on another job, just take a few months off and get onto the new one, keeping your options open to go back should things are not going to work your way.
It is critical to become part of a trade group a business networking group in your area, meet the members regularly, attend the meetings, listen to the speeches, there would be key people in the industry, economy, politicians, who share their knowledge, the business information, what they have done, what happened already and what they think would take place. You can also enroll in the business center of your library or your city designed to help people who set-up and operate their own businesses.
General business directories are available and some other directories can be bought to learn about the companies finances and all economic aspects. Always keep aware were you are and where you want to be as a business and the search for reliable business information, industry and the markets map is the best way to start with.