Start with Encyclopedias and Reference Books / eBooks: These resources will give you a broad overview of your subject and will allow you to better understand where the specific information you find later fits in the bigger picture.
Dive deep with Books/eBooks: Books/eBooks (a.k.a. monographs and secondary sources) will have more specific information about aspects of your topic. Sometimes there will be an entire book on your specific topic, sometimes you may have to assemble information from multiple monographs.
Interpret Primary Sources: Primary sources are things produced in the historical time period being studied. These can range from the written word, to artwork, coins, tools, and even everyday household objects. Interpreting primary sources will require the background knowledge gained through your reference and monograph research.
Find Images to engage your presentation audience: During your presentation, your words should be the focus, but sometimes an added picture really is worth 1000 words!
Supplement with Websites: Whenever you venture out on the internet, you need to carefully ensure the information you are finding is reliable. Ask yourself Who produced it, What are their qualifications, and Why they created what you are finding (including who funded it).