I started my prep with mgmat quan guides about a month ago, and recently moved on to the verbal section. After about 2-3 days of being immersed in CR and SC, when I went back to practice some quant stuff, I found myself forgetting key formulae.
So, I made myself this worksheet that I printed several hard-copies of, and now keep a copy handy...at work, at home, in the car...and try to answer each of these questions - AT LEAST ONCE every day.
Flashcards are good, and they serve their purpose; but I find that forcing myself to WRITE key formulae works better for my psyche and performance.
Another reason why I like this worksheet approach, while I can't carry flashcards around with me all the time (in my pocket), I print this worksheet "double-sided on one sheet of paper", and keep it on my person at all times...allowing me to work on it between meetings, or even when I'm in line at the deli, ordering lunch.
Lunch...umm...now, I'm hungry