The #1 thing that'll improve most people's workflow is learning how to use readline effectively. I'm continually amazed by how many people who use shells daily use the arrow keys to navigate around, don't know about common things like C-r to reverse-search through history and other commands that make editing on the command-line a breeze.
In aid of helping others along this path, here's a crib sheet I've found for readline shortcuts. I've been meaning to become more efficient in using bash and this might just be the push I need.
I've honestly tried to use the man pages for bash before, they are unarguably complete but unfortunately difficult to get started with. The chances of me knowing ahead of time to either search first for "readline" followed "Commands for Moving" or read the full man page until I get to line 2957 is slim.
This is almost a useful resource, but there are many bashisms on the list! Its utility is kind of limited for those of us who use a different shell when they don't have some sort of standardized "this only works in bash" warning.
I have the opposite complaint: I'm using bash, but thinks like mtr aren't part of coreutils, so I think of them as just separate programs that happen to work at the command-line. I could just as easily list ttyter as a command-line 'tool' for tweeting from the command line.
I don't really have a solution to this, because at the end of the day, the goal is to do more things at the command line, but it'd be nice to have a way to distinguish between features of the shell, features of the OS, and non-OS programs that have command-line interfaces. Even if I'm interested in all three, it's nice to know that 'sudo !!' can be expected to work machines than mtr, for example.
I love the autojump, but it's not exactly using a built-in *nix tool like most of these are. Would love to see more people open their eyes to how awesome autojump really is. Using cd to change directories is so broken.