Literacy about the terms within niche legal specializations. You understand what an attorney means when they say they need help with 'frogs', for example. Make them know that you're comfortable speaking with court clerks and that you are grounded in local rules and court services. The more expertise you can display about a pertinent niche to the firm, the more likely you are to be retained.
I can't tell you what every attorney will prefer in a potential hire, but my boss said my confidence and old school manners stood out to her. When I arrived at the interview, I handed her a professional copy of my resume and references. I was honest with her and myself about what I could do. I asked a lot of questions relevant to the job at the interview. After the interview I mailed a card thanking the firm for the opportunity to interview.
Great manners go a long way in business. When everyone is qualified, polite courteous behavior might put you at the top of the list.
Prior to working as a paralegal, I had a paralegal education, and I had worked at a title insurance company doing legal research and drafting legal documents