I usually ask them if I could watch them work. They always say yes. Then I watch what tools they use and how they use them and ask about them. They're always happy to tell me.

For example, I watched the cable guy install coax. I then bought the same tools he used, and later wired up the coax myself in the next house. I also watched tradesmen cut & sweat pipes, service my furnace, install molding, etc. All very interesting and useful.