"Business Necessity"

[hope_for_best]

I am filling for PERM and in the Form ETA9089 the section H-12 is rightfully "No". We have to provide a convincing Business Necessity justification. I would appreciate if somebody can suggest the "Dos and Don'ts" for Business Necessity justification.
Also are there any good sample for the Business Necessity Justification letter from which we all can benefit.

Thanks in advance...