You will learn the most by getting out there and getting some experience, trying different things and making mistakes and learning from them.
Second best is like redfox said, get out with an experienced trapper. That's also how I got into trapping in the first place.
There are a ton of books and videos out there, depending on what you want to trap. I would definitely suggest you get a subscription to The Trapper and predator caller and/or Fur Fish Game.