Perl Best Practices is a pretty good place to start - although it does have a little assumed knowledge...

Ultimately though, I'd just pick one of the books (eg the Camel book) and dive in and start writing Perl.

I found learning Perl in a "Read, Write, Read, Write" style quite good in that I tried to apply what I'd just read to the code I wrote. Also reading a book cover to cover, then going back through it a 2nd time - helped fill in a few gaps on some areas I didn't get the first time through

Hope this helps.

Update:
In my opinion, Perl is simply another tool in the toolbox, which may or may not replace your Shell scripts - depending on what you're trying to do. In the 'sysadmin' role, choosing the right tool for the job is just as important as knowing the tools themselves... Building code that is robust, efficient and maintainable is a delicate balance when solving a non-trivial task.