Pretty much the same way as fixing something else -- consulting the official manuals if you're a by-the-book type, or doing a complex job, with forums to provide practical (if not always letter correct) alternative methods, or more practical solutions.
The ETK parts catalog is among the best in the business, and freely available online, so it's easy to look up parts without owning a microfiche reader.
The ETM electrical schematics could be purchased over the counter.
I'm not up on the current system, but the old TIS factory manuals could be obtained on CD and installed locally. With everything now online, there is the subscription portal. But beware, like a lot of documentation aimed at pros, those instructions can be terse, and reference other procedures and documents that people in that position are expected to have access to and be familiar with. Not for hand holding or DIYers, but great for knowing a specific prodcure and expected specs and materials.
On the older cars, Bentley published quite comprehensive DIY manuals, based on the factory info. Higher quality than Haynes or certainly Chilton, though Haynes are still good.
To me, BMW completed their drift from what made them attractive to their core audience once the things like turbos and EPS appeared. And more single-use fasteners. The newest E36 is now more than 20 years old, and might feel a bit spartan to some. The E46 was a refined, more modern version. The E90 was more avant garde, but still had the good bones underneath, with normally aspirated engines and hydraulic power steering. Anything later than that is going to have EPS and feel like driving a video game. More comfortable and more gadgets, but not nearly as much fun or involving.
I dropped my CCA membership long ago, but in talking to a veteran member of a large chapter, even that demo has changed, and is less interested in the driving, and more in the modding, with cool stuff like CF.
They're rewarding, but require commitment, and won't tolerate short cuts. Cars that have been victimized by those things reflect it in their condition. Not different than any other European make.
