Use each other when referring to two people.
Example: Mike and Susan looked at each other.
Use one another when referring to more than two people.
Example: The four people in the car looked at one another.
Pronouns must agree in number and person with the words to which they refer.
Incorrect: Each drives their own car.
Correct: Each drives his own car.
Correct:Each [singular pronoun, the subject] of the women listed
See Affect, Effect.
Words that sound similar but that have different meanings may be used by mistake. Such words are called eggcorns.