Recently, we conducted interviews for a new Tech Writing position. Was I just being a perfectionist when I was shocked at the poor quality of some of the resumes and portfolios? A couple of applicants' work had dozens of errors: misaligned elements, inconsistencies, missing punctuation, and on and on and on.
I guess what I'm trying to say is: check your work before you submit it. Then double-check it. Then have at least two nit-pickers review it carefully.
Also, your portfolio should have docs that represent the type of doc typical of the job opening. If you are applying for a job writing maintenance manuals for hardware, and your portfolio contains just fluffy marketing docs, then you are at a real disadvantage. If necessary, create something just for your portfolio.