I know you're asking about the knowledge test, but what I'll say here may apply anyway -- take it or leave it, I'll just throw it out there:
Instrument flying is obviously very technical and a great deal of detail-oriented information must be kept top of mind. But as a pilot examiner, nearly all of my questions for the instrument rating ground portion (formerly known as the "oral") are built into practical and realistic scenarios which force the applicant to correlate knowledge rather than just recite information by rote. An unpleasant but necessary part of my job is occasionally having to issue a Notice of Disapproval during the ground portion of a practical test when it becomes clear the applicant can't do that. But in many cases they're hung up on what I perceive to be an "information retrieval roadblock." When I debrief flight instructors after these events I'll usually ask the CFI to look back upon the ground training provided to the student. I'll ask if the CFI, upon review of that training, could recall whether they required the student to "look up the answer" when he or she couldn't produce it. Usually, with a little digging, I'm able to determine that the ground sessions between instructor and applicant, regardless of the format they followed during the initial and intermediate stages of training, would ultimately resolve down to verbal quizzing in the days or weeks leading up to the practical test. And when the student would answer one of the instructor's questions incorrectly, the instructor would simply supply the correct answer.
A far better method of learning and retaining knowledge is digging into the associated reference material and producing the correct answer when stumped. For many (certainly not all) of the questions on instrument rating ground portion of the practical test, it's acceptable to "look up the answer" or at least round out a mostly complete answer by referencing the correct FAA publication. But when the applicant doesn't know where to look for the answer in the myriad of available publications and is left completely stumped as to how to apply knowledge, the ground portion simply grinds to a halt.
This is also a crude but effective way of ensuring every ground training session is "multi-channel," at least in a basic way, for the student. I'm a huge fan of multi-channel learning because it almost always works for any student if conducted properly. We all learn differently; some of us can simply read a textbook and "get it." Many of us could read that book fifty times and still not get it. We need someone to disambiguate information for us, i.e. an instructor, and/or we need the information to flow in and out of our brains via multiple learning paths. If we read, then discuss; discuss, then write; write, then draw; teach, then be taught to; ask questions, then be forced to find the information within the appropriate publication; at the right intervals and with the correct length of sessions, it's virtually guaranteed to be effective over time.
The huge additional benefit to this method is that the student becomes comfortable "traveling" through the appropriate publications to retrieve information. The more time you spend in the publications, the easier they are to "navigate," and the more sense you'll be able to make of the general framework. This pays off handsomely during that stressful time in a practical test in which one is called upon to come with the correct answer to a question and needs to use FAA publications to do it.
TLDR; Flash cards aren't enough. Look up the answer correctly and thoroughly whenever you're stumped. Get a buddy and exchange information verbally, in writing, by drawing, and by quizzing each other.
. There is competition for attention going on too, work has been pretty harsh, need this break time.
