This sounds obvious, but before you start any research, make sure that you review the client's file. Analyze the facts in the client's file and try to frame the legal issues (who the client is, what jurisdiction you're in, what law applies, etc). Next, you need to figure out what you already know and what you need to learn. Take note of any primary law that you have been given. Finally, using this information, generate some search terms.
Secondary sources are incredibly helpful because they can give you a basic understanding of an area of law. Secondary sources can direct you to terms of art and relevant primary sources, which can help you narrow your research, or compare how different jurisdictions have analyzed a legal topic.
There are different types of secondary sources, and the best secondary source to start with will depend on your familiarity with the legal concept and what you are ultimately looking for (e.g. scholarly v. more practical legal information). Here is a list of the different legal resources:
Google, and other search engines, can be a great tool for finding relevant legal information, especially about emerging legal topics. However, always remember to think critically about information you find via Google and that a Google search should never the end of your research.
The goal of reviewing secondary sources is to: (a) understand the background of the law, and (b) find appropriate primary law (current case law, statutes, regulations, etc). You might find that you are seeing the same cases and statutes cited in different secondary sources, and that is a good thing. Once you're at that point, you can start using your case research tools, statutory research tools, or other research tools.
Research Tip - Research is Not Linear: Legal research is not a linear process. It's very possible that once you start delving into the primary sources, you will have to go back to the secondary sources. Make sure you keep track of your search terms, and if you need assistance, don't hesitate to contact a reference librarian!