In my opinion, you will never have enough reference material, and you will never be able to answer every question off the top of your head.
I am also somewhat new to the field, although I have nearly 10 years as a control systems engineer, and a few years as an industrial electrician apprentice before that, I still am constantly refreshing my knowledge. The rate at which the technology changes is stagering, and to keep on top of things you need a good resource network. Periodicals (Control engineering magazine comes to mind) have a lot of information and past issues online. You can sign up for their newsletters and once a week or so they will send out emails with articals, both new and old that will give you a random busrt of relevant inspiration, or make you remember something you have been applying out of instinct.
Liptak's is invaluable, but won't keep you up to date, and will put you to sleep more than once. They are a really good shelf reference though.
I would suggest you start by getting to know the processes you work with intimately, read up on the controls used and their functions outside of the obvious application, both the theoretical controls and the hardware. Look at applications of that hardware outside of your field, Google will help with this. As JLSeagull said manuals can be really helpful. The manual for the Watlow 96 series controller got me through my first 6 months of PID tuning and programming in real life, and I still have a copy of it on my computer.
After you know your processes well enough to shoot answers at your boss, start going outside of that realm and look for relevant things you can bring in.
Also if you don't have a lot of experience with hands on get out on the wrenches for a while, tune some loops by hand, basically spend some time getting your hands dirty in the field. Nothing beats field work for getting to know your processes.