Union apprenticeship sign-ups near Baltimore

The training centre near Baltimore opened applications for apprenticeships in electrical and welding trades. I am in Baltimore, in case local advice matters. The application needs a diploma or equivalent, a driver's licence and a short aptitude test. What do you wish you had known?

The aptitude test was mostly maths and reading a diagram. Free practice tests online were enough for me.

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