Q. What can I do to make sure I’m not accidentally plagiarizing?

You’re right, you can’t know everything there is to know; however, you can keep track of the sources you’ve referred to in your research and make sure that you’re making respectful choices in how you cite those authors’ works in your research. Here are some suggestions:

Be familiar with the significant authors in your field

If you’re seeing the same names being cited in many of the sources you’re referring to, it’s likely those people are the significant authors in your area of research. Becoming familiar with their ideas, where they published them, and who else is frequently citing them is a good way to inform yourself of some of the major discussions happening in the research. Having that awareness will lessen the likelihood of accidentally plagiarizing those authors' ideas.

Keep track of the works you refer to

Citation managers are great tools for keeping those records and they can also help with creating preliminary versions of in-text citations and references. 

When in doubt, cite a source

If you’re sure the information isn’t your original work but you’re not sure where your information came from, find a source that verifies the information and cite that source. See also What is common knowledge? 

Be prepared to explain your process

If your original ideas are coincidentally similar to the works of other scholars, your instructor may ask you to explain your process to better understand how you developed your ideas. Be prepared for those types of conversations by keeping track as you’re doing the work e.g., what information did you gather versus what were your original ideas? What sources did you refer to, even if you didn’t quote or paraphrase from them? What was information you already knew before you started research for the assignment/project versus new knowledge you gained as a result of your research? Showing your work will help your instructor understand how you reached your conclusions.