Use Chicago Style, and stick to one "flavor" of Chicago
Chicago is the discipline standard citation style for historians, and should generally be your first choice when writing history papers. While Chicago has several different variants to choose from (author-date, footnote citations, etc.), it is best not to mix them, to keep the styling of your paper clear and consistent.
Use a Citation Manager
Citation management software allows you to quickly collect citation information for interesting items you find online, while also allowing you to track and organize this information long-term. Additionally, citation managers can automatically generate citations in the style of you choice, saving you the hassle of writing them yourself. See more info below.