If you use this method and do it correctly, you can't accidentally plagiarize. Like, it's impossible to mess up if you do this.
Sloppy note-taking can really get you in trouble, so invest some time in taking careful notes.
Here's an old school note-taking method that people have been using for eons. Use this, adapt it, or develop your own system.
You'll need index cards, different colored pens/highlighters, and your sources.
Your cards could look something like this:
Write the citation, or some code for the citation info, like the author's last name and first few words of the title. Include the page number(s) too. If you use a code, be sure to have the complete citation info somewhere for later use.
Using a note-taking system like this will help you:
Need more? See Resources for UCLA Students.