Of all the troublesome pairs of words in the English language, affect and effect rate at the top of the list—for good reason. Both words sound alike, are related in meaning, and can be used as either subject or verb. But there are easy ways to distinguish them and determine which word you want.

Affect is a verb meaning “to influence.” Use it in any form whenever you have that idea in mind.
Examples:      
The weather affects my sinuses.
Our new policy will affect the way we do business.
The affected employees will adjust their work schedules.

Effect is usually a noun meaning “result or consequence”; it is often indicated in a sentence by its use with a, an, or the.
Examples:        
What is the effect of the weather upon your sinuses?
What is the overall effect of the new policy?  
An important effect of the decision was better morale.

Effect can be also be used as a verb with the limited meaning of “to bring about”; it is often associated with the idea of change.
Examples:         
The company effected a policy change.
We must effect changes in our safety regulations.

Additionally, if you use the suffix –ive in business writing, the word you always want is effective.
Examples: effective measures, effective date, effective managers.

You should note, however, that forms of the word affect have other meanings in the sphere of human behavior. We speak of a person’s affect (the way one comes across emotionally) or one’s affectation (artificial behavior), but these are not uses that you need to consider in your business communication.

Remember:

affect – verb – to influence (also with –ed,-ing,-s)

effect – noun – result or consequence

– verb – to bring about (also with –ed, -ing, -s)

effective – always e in business writing.