Understand the differences in usage between their, they're, and there.
Learn the distinction between your (possessive) and you're (you are).
Differentiate between its (possessive) and it's (it is or it has).
Grasp the meanings and usages of to, too, and two in sentences.
Know when to use accept (receive) and except (excluding).
Recognize how affect (verb) and effect (noun) differ.
Learn when to use then (time) and than (comparison).