Affect--as in emotional (try associating it with affection).
"His affect was one of a sad clown."-- This is an emotional change so affected.
Affect can also mean 'to copy'. So you could also say 'Thomas affected the manner of a gorilla'.
Effect is much more straight forward.
Effect-- as in cause and effect. Not emotional change but some sort of more physical or or relational change.
"The impact of the car effected the stability of the wall."
Or even 'The wall was effected by the impact of the car.'
The car hitting the wall CAUSED the EFFECT of making the wall weak. Neither the wall or the car had any emotional response to the accident. This is a statement of cause and effect--EFFECT.
This isn't perfect but it helps. Affect equals emotion so think of affection. If it's not emotional, it's not affect.