1) Learn what the company does. Read the wikipedia page, look up their presentations for their customers, look what their write about their business on their web site, look what others write about the company’s field of work.
2) Learn how is their business doind financially. Read their 10-K on the sec.gov ; you can get a quick overview on yahoo finance, but there’s not enough and they do make mistakes. If you don’t understand it, you need to learn about general corporate finance more.
3) Learn what the company’s management says. Read their investor relations pages – look for what their long term plans are. Read a transcript of the last two quarterly conference calls. If you don’t understand what they are saying, you probably need to repeat 1) again and learn their business better.
4) Research their market and competition. There’s usually specialized publications for different types of businesses. Read the investor relations of their biggest competitors.