I was flipping through my ragged copy of The Elements of Style, when one of Strunk & White's tips caught my eye "Put statements in positive form."

Simple enough isn't it?

Sometimes we use "not" to negate what follows. Sometimes we abuse the negative to qualify the words that follow. In either case, we weaken our writing.

Write what you have done, not what you haven't done. Compare:

•  I did not believe that volunteering in the ER was a good use of time and decided not to pursue that in favor of work for the Suicide Prevention Hotline.
• I knew I would learn more working for the local Suicide Prevention Hotline than pushing gurneys in the ER and chose the former.

Or.

• Our start-up's resources did not fully match those of our competition and we could not effectively compete in the market place so ultimately we were forced to cease operations.
•  Lacking capital, our start-up failed to market  itself well and was forced to close its doors.
  

In both the examples, the positive statement is livelier and much more succinct, a critical factor when dealing with tight limits.

So put the punch and power back in your writing. Be positive.