I consider hashes to be part of the basics... so that might be a good start... (if you don't know them already)

What you do after that is up to you, as in, what do you need? if you need to use OO then references (or atleast the tutorial) and objects might be a good path

And what about regular expressions? they are quite useful... (or atleast IMHO), do you know them? (as in the more 'advanced' stuff like, look-aheads, look-behinds, non-capturing groups (not that this is really advanced, but you should know (and use!) them aswell), ...)

But if you ask me what the most important thing in the perl world is then I would say: `perldoc perlstyle` (or atleast the basic things of that). Coding without a decent style (like indenting things) results in useless code.