I usually ask myself, if I change the word to "create" or "change", which one makes more sense? Are you creating perception or changing perception? Change is affect, create is effect.
It might not work in all sentences, but it's easy to remember which is which - affect has a C in it, and change starts with C.
But...but...but...effect has a c in it, too!
And... AND... "Change" and "Create" both start with "C"! The way I always remember it is that one may affect
, which is kind of a shorthand way of saying that when you affect
a situation, you have had an effect
on it. Just remember it's in alphabetical order.