Affect / Effect

This is a tough one for many people, including some professional writers.  Generally, affect is a verb and effect is a noun.  When you affect something, you have an effect on it.  The mistake most often made is writing affect instead of effect.  Stick with me here and refer back when needed -- once you set your mind to it, you'll see it's really not too hard.

Affect means to act upon or to move -- the photos affected me so much I cried.   It also can mean to pretend -- on her first day of high school, she affected a calm she did not feel.

An effect is a result, a consequence.  The well-written blog had quite an effect on me.

More examples of the correct use of effect:  Movies are full of sound effects and other special effects.  Your house is full of your personal effects.  When things become effective, they go into effect or they take effect.  I strongly disagreed and wrote her to that effect.  On Halloween, I turned down the lights and put on spooky music, but it was all for effect.  Cause and effect.

Of course, to throw a monkey wrench into the works, effect can (rarely) be a verb, most often when talking about change -- President Obama's administration seems to be finding it tough to effect true change.  In this sense, it means to make happen, to create.

Psychologists may speak of a person's affect, with the accent on the first syllable (AFF-ect).  This refers to a person's emotional response.  I've never used it this way in my lifetime, and I'm guessing you probably won't either.