What it is
Free recall is the process of taking everything you can remember about a topic and dumping it out of your head onto paper some time after you tried to learn it.
How to do it
Set aside time on your calendar sometime after you've completed a learning session. For example, if you're reading a journal article for class today, set aside time in a week.
When the time comes, don't look at your notes or the article or any other source material. Instead, start with a blank page, and write down everything you can remember about the topic. Give yourself time to poke around the dusty corners of your mind for any pieces that might have gotten lost back there. Really think through it and get as much down as you can.
Then, open your notes and your textbooks and so on. Compare what you wrote down with what the material actually contained. Do they match? Note where you remembered something that wasn't true, so you can reinforce the correct information. Then go over the source material, and fill in the places that you missed, again noting areas for further reinforcement.
More information about how to overwrite wrong memories and how to get slippery things to stick in your mind better, check out Mnemonics.
When to use it
Some amount of time after a study session. How much time? Spaced repetition can help with that. This also makes sense to use when starting to study for a final exam. Make the most of your study time by focusing on areas that free recall identifies as weak spots.
A quick variation of this when first learning the material is to use Awkward selfies. If you want to use a partner instead of a page, check out the Feynman technique. If you're doing this, you really do need to write it down, in order to avoid Recall vs Recognition.
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