As an author, I come across words all the time, which people frequently confuse. Among those are

Affect = a verb meaning to influence
Effect = a noun meaning result
Effect = a verb meaning to cause an action
The explosive sound affected the crowd’s behavior.
The Cavs fans had little effect on the Miami Heat’s play.
The administration has effected how we see ourselves as students.

Agree To = used when referring to things
Agree With = used when referring to people
We agreed to the changes in policy.
We agreed with the experts in the field.

Amount = an indefinite quantity (cannot be counted)
Number = a quantity which can be counted
The amount of news consumed by individuals each day varies.
The number of people at the malls on Black Friday increased.

Backward is ALWAYS used; never use Backwards.
She stumbled backward into the arms of the man she loved.

Envelop = means to surround
Envelope = the paper wrapper for a letter

Ensure = to guarantee or to make certain
Insure = to purchase protection for life, health, etc.
Even an expensive stereo system cannot ensure good quality sound.
I will insure the package’s contents when I ship it.

Lead = a soft, heavy material
Lead = to guide, show the way, to be in command of
Led = past tense of the verb “lead”

Passed = is a verb
Past = is never a verb (can be a preposition, a noun, or an adjective)
He passed his test.
I walked past the cemetery on my way here.
In my past, I have done things of which I am not proud.
In the past year, my career has changed dramatically.

So, what words and phrases confuse you? Do you have some such as “lie” and “lay,” which forever plague you?