I can still draw the entire circle of fifths from memory. This is a well-known diagram demonstrating key signatures (i.e. F major or b minor) and their relationship to each other.
(The next paragraph may be boring for musicians and incomprehensible to anyone else. Sorry.)
For me, reconstructing the diagram boiled down to the mnemonic Father Charles Goes Down And Ends Battle (the order in which sharps are added to a key signature), which reverses nicely as Battle Ends And Down Goes Charles Father for flats. The order also works for the key names outright, provided you know where C belongs and which direction to go with the rest. There are fiddly bits at the bottom with the three enharmonic keys but muscling that out is just something one does once and never worries about again. Finally the relative minors are achieved with a 90º twist of the clock face counterclockwise, so to speak. At least, thats how I think about adding three flats.
I would scan it in so my mother could print it out and hang it on her refrigerator door, but its on the back of a folder which is too large to fit in my scanner. Ill make the poster version in January.