The most common verbal errors spread the way the common cold does: One person picks it up from another, usually quite casually. The next thing you know, nearly everybody’s infected.
I compare these transgressions to a cold, as I am likening the two elements. Think of this: The critic compared his voice to that of Caruso. To draw a contrast, I would use compare with. “Caruso was a great singer, compared with you, Larry; you howl like an alley cat in labor.”
So, let’s treat the linguistic outbreaks—with some usage antibiotics.
Here’s hoping they will affect you positively, yielding a salubrious effect. Wow. These two near-homonyms are tough, because each can be used as a noun or a verb. Those are just the most common usages for each.
Effect as a verb is to bring about, as in to effect change.
Affect as a noun—pronounced AFF-ect—denotes a person’s emotional state, especially when it’s visible. This one is probably of little use to you—unless you’re a clinical psychologist—except for the purposes of recognizing its misuse: “Hey, Smitty, you spelled effect with an A, you yucklehead!” That’ll affect his affect, all right—and quite effectively, at that.