Just keep a good attitude. Honestly I've been a labourer for 17 years. Never picked a trade. Reason being esp for larger companies. Is days never the same. So if your going to start at the bottom. Enjoy it while you can. Most of the pressure won't be on you. It'll be on the actual tradesman. So pay attention. Ya can never be to safe. That's the one thing I learned working for Aston Construction in Arizona @ Kearny smelter.

If your going to be doing labourer. Your job well most likely consist depending on the company's project and size. Doing random stuff every day.

Like one day I'd be helping pipe fitters, next Carpenters, next electricians. Everyday was different. Your not supposed to know everything. You'll learn. Your most likely pick up trash, "stage" areas(that's another big thing you'll need to do/learn to do right). Or you'll do stuff like firewatch. Move generators around. Cleaned up after messy ass Carpenters. Just keep safety a priority. Big boss we'll watch for that. Big determination if they well keep you are not. Don't try to be badass or a hero. And don't ever fuck up finished product.