It takes more than three weeks to prepare a good impromptu speech.
--Mark Twain

Advertisement:
A 60-second radio ad should repeat the product's name at least five times.

Billboard:
The text should consist of six or fewer words.

Business letter:
Keep it to one page.

Characters:
Avoid giving two characters similar-sounding names and have each major character's name start with a different letter.

Descriptive writing:
As to the adjective: when in doubt, strike it out.
--Mark Twain

Dialogue tags:
If tags are omitted in three or more speeches in succession, readers will often be confused about who is talking.

Junk mail:
In an advertising letter (junk mail), the P.S. will often be the only part that is read.

Productivity:
Three hours a day will produce as much as a man ought to write.
--Anthony Trollope

Radio commercial:
Say something interesting in the first three seconds.
--Jay Levinson

Readability:
--A text whose sentences average 10 words will be understood by an average fifth grader.
--The greater the average number of syllables per word, the harder the text is to understand.
--If the same quantity of text is printed in a narrow column and a wider column, it will be read faster in the narrow column.

Screenplay:
One page of the script equals one minute of screen time.

Speech writing:
Each minute of a speech requires about 125 words.

Word count:
A double-spaced typed page will contain about 250 words. The count depends on the font, type size, and margins.

Wording:
Your style will seem stuffy if on a page you use more than one word that you wouldn't use when talking to a friend.