Upgrade from merely skimming encyclopedias for ideas or only mining the recommended reading list--historians analyze encyclopedia articles closely to understand the context of their topic and identify where a topic is either explored or unexplored (which one you choose depends on your goals).
Start noticing the different types of encyclopedias available to historians. There are more types than general, such as Encyclopedia Britannica (which is still useful); if you search Credo Reference, you'll see all types show up in the results, and you'll need to know what you're seeing.
Below are linked a few different kinds of encyclopedias--read the descriptions to understand the purpose.
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