I really don't know much about Slackware, or even Linux in general. I'm just your average user who has picked up a book, read a lot online, and has had to work out several problems. If you're really serious about it, you'll pass me up in no time
. Read a lot on this forum, there's some good information here and really helpful/friendly people.
The online Slackware book: http://www.slackbook.org
(Lots of Slack-related info here)
Making your own packages: http://www.linuxpackages.net/howto.p...erfect+Package
(This'll give you a good idea of how to go about making packages for Slack. Some things, like the naming scheme, is linuxpackages.net specific, but you'll still learn a bit)
The book titled "Running Linux" by O'Reilly contains lots of information, not specific to any distro. I think the best way to go about learning Slack is to learn Linux in general, because it's not a distro with all the fancy GUI tools that are distro-specific. Like they say, "If you want to learn Red Hat, use Red Hat. If you want to learn Linux, use Slackware."
I also think learning to program in C/C++ would be very beneficial to learning Linux. I can't really vouch for this since I haven't delved into programming yet, but it seems like it would help greatly. And...don't forget to learn your shell...probably bash.
There's so much information out there, just look around. I've barely touched on the subject. Sometimes learning one thing will lead to another, just go with it.