Write down as close to everything as you can. I rarely actually look at these notes, just writing everything down is usually sufficient.

If you forget stuff afterwards, go back to the notes and transfer the stuff you forgot to a shorter list. Again just making the list is often enough.

If you really need to know it, find a way to use the information, even if it's a bullshit use (alphabetize it, make a timeline, make a list of other concepts that depend on this concept, whatever). But if that fails and you really do need to memorize a big list of raw information, like the periodic table or something, then use flash cards.