I'm of the school of thought that emphasizes the theory on how things work and how you work on them. Then you figure out the details.

For an engine, you always check for air, spark, fuel. There are standard troubleshooting steps. You squirt some starter fluid in the thing. It fires for a second. That means you have air and spark (because it fired) but somehow the fuel isn't getting in there (because you had to squirt starter fluid in to get it to fire - you added the fuel manually). Now you can check the fuel system.

Likewise bikes have basically two things - cable actuated levers (derailleurs, brakes) or bearing preload stuff (BB, headset, hubs, although all are relatively simple with cartridge bearings). I'm skipping electronic because I haven't work on it.

So cable stuff - the cable pulls. It starts with the cable pulled all the way out. You pull it with a lever until it stops, either because the brake pads are clamped tight or the limit screw limits travel. Did it go too far? Not far enough? Did it start too far? Not far enough? Now you can adjust the start point, the end point. For indexed shifting you can consider the each click a separate end point. Too far? Not far enough? Go from there.

Bearings are similar. There's too loose, too tight. Start at too loose, tighten until it's not too loose. Don't start at too tight because you are squashing the bearings and the races together and one or both will become imperfect (usually the races).

Now you can trouble shoot any kind of brake, shifter, or bearing thing. All you have to do is figure out what limits what, what tightens what.

If you learn by rote ("Turn this screw if it's too far this way") then you run into the problem of "These screws aren't where they're supposed to be!". Or, worse, the screws are reversed for some reason, so, say, your rear derailleur ends up in the spokes or your crank rips your front derailleur off the frame.

Rote is bad.

cdr