Symbols
Percent vs.%
In copy that contains many numbers and in non-narrative copy where space is at a premium, use %. In other copy, use percent.
And vs. &
Do not use the ampersand except in titles such as company names in which the symbol actually appears and in non-narrative copy where space is extremely limited.
x
Never use x to mean by.
Example: a ten-by-twelve-foot room.
#
Never use # for Number. Use the abbreviation No. when necessary; but it is often superfluous.
Never use # for pounds. Use lb instead.