As an interviewer I look for a few things.

A clean 1-2 page resume, the first thing I do is look at your resume and see what you have been up to the last few years. It doesn't have to be fancy but it shows you prepared, bring multiple copies of everything, there will be multiple interviewers from the field and management. Bring proof of everything on that resume, transcripts, current certs, letter of recommendations, the more you bring the better. This is a career interview not just a job interview, how prepared you are speaks volumes.

How did you find out about the trade? And what do you know about the work we do.

Be able to talk about your ability to work with tools and do hands on work. I've interviewed NASA scientists to dog walkers, tell me why you want to do our work and don't tell me because it pays well. Prepare to speak about things not on your resume that apply to hands on work. Hobbies etc.

Hope this helps, I know its a nerve racking process. Think of a way to stand out beyond the other hundreds of people being interviewed. Realize that this is a small proud trade and we want what is best for the future.