With expert knowledge of the content of information resources (and knowledge of the limitations as well), the professional knows "the best" resources for a specific area.  After fully understanding the problem, a systematic collection of information follow, which in turn leads to analysis and synthesis, and a deliverable (often a report).

Researching a publicly owned company: Aside from US-based public companies, which may be traded on stock markets, companies also may be traded on foreign stock exchanges.  Below are two resources to find a list of foreign exchanges -

http://www.tdd.It/slnews/Stock_Exchanges/Stock.Exchanges.htm

http://en.wikipedia.org/wiki/List_of_stock_exchanges

There are three primary regulatory agencies that oversee regulatory and compliance issues with publicly traded securities or with security dealers.  There is the Security & Exchange Commission (SEC) - www.sec.gov, and Financial Industry Regulatory Authority (FINRA) - www.finra.org, and National Futures Association (NFA) www.nfa.futures.org.   FINRA was formerly the National Association of Securities Dealers or NASD.   FINRA is the largest non-government regulator for all securities firms doing business in the United States.  

When researching overseas companies, try to locate an investigator in that particular country who can assist you in understanding the legal system there, and help you conduct the research on-site. Two very well regarded, though expensive database sources used to investigate people and companies is Capital IQ - www.capitaliq.com, and www.boardex.com from Management Diagnostics Limited.