One thing I've never really gotten a handle on is the "laborer" economy, and despite being at near constant war, I keep running out.

The key is specialization and happiness management. You basically want to have raw material provinces where you throw all your labour, and focus on things that reduce unrest in those places to minimize losses turn over turn. Concentrating them in the appropriate places and keeping those places locked down reduces the turn-over-turn loss.

I also usually end up sending out caravans mostly to get back labourers, a continuous feed into my machine that is better optimized and more productive than any of the trade routes could match. I end up with a surplus of raw materials so it can feed back into keeping labour up.