From Strunk & White’s Elements of Style: “Make definite assertions. Avoid tame, colorless, hesitating, noncommittal language. Use the word not as a means of denial or in antithesis, never as a means of evasion.”
Instead of this . . .
Say this . . .
He was not very often on time.
He usually came late.
She did not think that alphabetizing the emails was a sensible way to use her time.
She thought that alphabetizing the emails
Not all of the barrels had been inspected.
Some of the barrels had not been inspected.
Not coming to work on time is a bad habit.
Coming to work late is a bad habit.