I don’t know about you, but I ALWAYS need to brush up on some of these tricky words! I hate it when my editor’s the one to catch them!
Affect/Effect: “Affect" is a verb; “effect” is usually a noun that sometimes means “to render”.
As/Like: “As” is a metaphor and should not be used in place of that, whether or like; “like” is a preposition/simile. Use “like” only when comparing two things.
Between you and I/Between you and me: “Between you and me” is the only correct usage.
Eager/Anxious: You’re “eager” when you’re looking forward to something; “anxious” is when you’re dreading something.
Elude/allude: “Elude” means to evade, to foil; “allude” means to refer to indirectly.
Farther/Further: “Farther” is actually measurable distance. “Further” is metaphorical distance.
Fewer/Less: “Fewer” refers to things that can be counted. “Less” refers to things that can’t be counted, to degree, or value.
Implied/Inferred: The person speaking “implies” things which are not actually spelled out. Imply means to express indirectly, to hint at. The person listening “infers” things which were not spelled out. Infer means to surmise, to derive as a consequence.
In between/Between: “In” is superfluous.
Lay/Lie: “Lay” is a transitive verb meaning “to cause to lie” (lay, laid); “lie” is an intransitive verb meaning “to be at rest” (lie, lay, lain).
Regardless/Irregardless: There is no such word as “irregardless”. (Just ask your spell-checker.)
Set/Sit: “Set” means to cause to sit and requires an object; “sit” means to be seated.
Which/Who: “Who” or “that” refer to a person. “Which” or “what” refer to an object or situation.