I always just used my left hand with the thumb and pinky as the y and x axes respectively, then the in-between fingers just help me visualize which "point" is higher (we only have two options to choose from if they're not equal anyways)

I'm not sure I understand your mnemonic. It looks like you've got 1/sqrt(3) as one of your exact value for sine and cosine... but that surely isn't right.