I’m often asked about the difference between these two words. When I go into a great speech about their real difference – ‘effect’ is a noun, ‘affect’ is a verb – I tend to get blank looks back. So I explain that something affects something else to produce an effect. Still nothing.
Even I if go back to primary school definitions, that one is a ‘doing’ word while the other is a ‘thing’, there is still incomprehension. It’s generally difficult to explain the finer points of language to people who don’t know what verbs, adjectives and nouns are.
When someone I was explaining this to the other day finally got the idea, they said “Ah, I’ll just remember ‘special effects’ in future.” And that seemed to do the trick.
So, if you’re stuck, remember that special effects are things, so if what you’re talking about is a thing, use ‘effect’. Any other case, use ‘affect’.