I'm not so sure that's the lesson...
I'd be interested to know what Mr. Eagles process was, but my suspicion is that there was an early period of experimentation with a broader range of material that he then edited down and chose the pieces to focus on
My sense is that early on is the time to experiment...put different things in front of different audiences and get a feel for the kind of stuff that plays strong for you...then that's the material you focus in on -- get inside of...but there's no way to find out what your "four tricks" are by sitting alone with a book
What I did when I was first building my stand-up show, and I recommend it to anyone, was I did a 10 minute spot at a local comedy club every week. I worked in a new piece every 3-4 weeks, videotaped each set, and after 3-4 performances of each new piece I watched the tape and made a decision about whether to cut it, table it, or pursue it further.
You surprise yourself. There is stuff that reads great, but plays flat (at least in my hands); and stuff that reads flat, and plays really strong.
What you're looking for is strong material that let's you showcase your personality and build a relationship with them...because you're so close to yourself, it's difficult to understand what you're personality is and what they see when they look at you on stage...so the way to find material is to play, throw stuff on the wall and see what sticks
I would stay away from performing some things in 13 steps (contact reading) that require a baseline of performing experience and confidence
But yeah, practice the stuff, see what you like...then, of that stuff, see what they like -- and those are the small number of tricks you build your career on
and, most importantly in my view, get a "lab" ... a venue where you can play, experiment, learn...