Union apprenticeship sign-ups near Baltimore - first time posting

The training centre near Baltimore opened applications for apprenticeships in electrical and welding trades. I do not usually post, so bear with me. Classes are in the evening and work is during the day. 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 saved me later.