It's almost always fine to start by looking for a book in the library's online catalog. Here are some additional suggestions:
If you are unfamiliar with your subject area, it will be very helpful to begin with a source that summarizes the main events or circumstances and also describes the historical context. This strategy also helps you verify that at least some research has already been done on your topic--it would be very difficult to cover all the background and conduct original research on your topic without any direction from other scholars, all in a single semester!
You can find print reference sources such as encyclopedias, especially subject-specific encyclopedias, published bibliographies, and general histories, that provide broad overviews, in the History, Philosophy, and Newspaper Library.
Many of these are available online, on our Guide to Online Reference Sources:
Some multi-disciplinary online reference collections are:
Wikipedia and other crowd-sourced online encyclopedias can be very useful. Bear in mind, though, that they have not always gone through the same rigorous review process as traditional reference works such as the ones listed above; the articles are also often not written by experts. Some Wikipedia articles, especially on controversial topics, are constantly being re-edited, which can be good (they're updated) but can also be bad (editors disagree over the content, so it changes frequently and you may not be able to find information that you found earlier).
If you use Wikipedia as a source of information, make sure you follow up the references (footnotes) to confirm that the author used legitimate sources to compile the entry. You should also look at the "talk" page (find the "talk" tab in the upper left corner next to the Wikipedia logo) to see how controversial (or not) the article is, how many people have contributed to it, and what kinds of discussions they are having. Here's an example of a particularly messy one: Wikipedia "talk" page for Armenian Genocide article.
Google Scholar is most effectively used as a supplement to other search strategies. Historical Abstracts and America: History and Life remain the standard "first-stop" article indexes for historical research.
What does Google Scholar Search? Google doesn't disclose what exactly it does and does not search. It does search online journal collections, like JSTOR, Project Muse, and the output of major online publishers like Oxford University Press and Wiley-Blackwell. It doesn't search all the online journal collections you can access through the Library. For example, as of this writing, it does not search Periodical Archives Online, a major collection of journal backfiles in the humanities and social sciences. Similarly, while Google Scholar searches government-produced article indexes like PubMed and ERIC, it does not search commercially produced article indexes like Historical Abstracts, America: History and Life, MLA Bibliography, or Reader's Guide Retrospective.
Once you have decided on your research topic, and gathered some basic background information, you should also make a research plan. The usual starting point is to identify the main currents of thought on your topic. Naturally, you need to know which historians have taken up this topic, what their main arguments are, and how our understanding of the subject has changed with shifts in the predominant methodologies and theoretical perspectives in the historical profession. In answering these questions, you will use secondary sources (the published work of scholars specializing in the topic), also known as secondary literature, on the subject. You will situate yourself in relation to the secondary literature on your topic. Does your analysis agree with previous scholarship, or are you offering a new interpretation?
For more on secondary sources, continue on to the next page of this guide...