Some writers make the mistake of using a double negative. Examples of double negatives are:
"Don't ask me for nothing."
(Correction: Don't ask me for anything.)
"We don't have nothing."
(Correction: We don't have anything, or, We have nothing.)
"Can't nobody hold me down."
(Correction: No one can hold me down.)
In the last sentence, not only is the grammar atrocious, but the syntax is wrong. Proper sentence construction is a must if the writer is to be taken seriously.
Then there is that rare bird, the triple negative. For example:
"I'm not battling nobody no more."
(Correction: I am no longer battling anyone.)
Remember to avoid the double or triple negative at all costs. There is no need to go for added emphasis. A single "negative" will suffice.