Initially, books along with using Linux. Then, as you mentioned earlier, trial by fire. I started with RedHat when win98se pissed me off for the last time. I just said "fuck it", fdisked my desktop's hard drive and decided to learn Linux. Once I learned the basics, I switched distros to Mandrake. Got comfortable with that, switched to SuSE. Stuck with SuSE for a bit and then decided to try a distro called Sorcerer.
While I would generally not recommend that path, if you can work it out, brilliant.I went right to gentoo knowing literally nothing about Linux (besides knowing a little about POSIX) after I couldn't get RedHat installed because the installation script failed somewhere because of my hardware. Everyone can just jump right to gentoo. It's really not all that hard if you have any kind of attention span and patience. The "lol you compile stuff all day" argument doesn't even matter anymore, even "old" and underpowered ARM boards are fast enough to handle it and on modern computers it really doesn't matter. Gentoo's capability of avoiding "features" included in software through use flags to trim down bloat is now more relevant than it ever was.
That being said, if you have the fitting hardware, maybe try one of the *BSDs first. Linux userland regarding critical software is going downhill with no signs of stopping.
I have the kernel save its config file in /proc/config.gz, so on any kernel update, I'll symlink the new kernel to /usr/src/linux then run zcat /proc/config.gz > /usr/src/linux/.config followed by a make oldconfig. With any new options being shown during the oldconfig. I like to verify afterwards with make menuconfig to ensure that I've understood what ever new options were shown.Also you can sit down and roll a custom kernel for your hardware and usually only have to very slightly touch it for later hardware updates. This used to be easier back in the day since the kernel has become a lot more complex with a lot more options, but if you are a bit hardware literate and read the option descriptions, that also is mostly a game of patience