This is a tough one. The best way to learn is through an apprenticeship. There's very little out there in book knowledge for what you are asking for. You could look if you cared to at some of the products that are out there, but I would think that would be too difficult because there's too many products on the market, like thousands of them. Some things you may never use while others you'll use daily.
I apprenticed with a company that did mostly industrial (translation: lots of pipe bending with ridgid), but we also did quite a fair share of commercial work and only a little residential. The first 2 years was nothing but learning supplies so you were a go-for for at least that time. Learning products and their names and their sizes and where they go, etc... I did a great deal of service work cutting holes in panels for pipe and whatnot, all under a watchful eye of a mechanic. Sounds easy, but without a lot of calculations one mistake can ruin a whole panel.
The only place to start is at the bottom -- and was I way at the bottom. I have some war stories for you all.
BTW, it's easier to go from where I am to residential but it's not as easy as it looks. As an electrician I am top notch. As a mechanic getting things done the easiest and quickest way in residential, not so much.