How important is it to avoid double negation in English?

Very!  In English a double negative = a positive.

I'm not not coming. = I'm coming.

She didn't buy none. = She bought some.

Confusing?!?  I know. In some varieties of English you can use double negatives for emphasis. You may have heard these on television or in a film. Technically speaking, you can only use one. You could not be misunderstood (you would be understood!).

Which resources did you use to find the solution? Were the resources useful?