Union apprenticeship sign-ups near Detroit - any advice?

I heard of an apprenticeship with paid on-the-job training for people changing careers. There are 4 people counting on me, so I am trying to be careful. The application needs a diploma or equivalent, a driver's licence and a short aptitude test. What do you wish you had known?

Keep everything in writing and save the confirmation numbers. It made the follow-up calls so much easier.