These 2 books often get mentioned. They're quite high level. I found HOP fairly tough going but well worth it. At about that level I absolutely love Perl Hacks and particularly APP2. They're a good read, and guide you through lot's of wonderful Perl trickery. I feel they still work as tutorials even so. HOP, by contrast, concentrates on the functional programming you can do in Perl. Really great book, though.

At a slightly lower level, I tend to think (this is going to sound *very* trite) that the best way to learn is by having fun. (yuck). If you enjoy discovering things, they'll stick. Also, some people prefer books, some people prefer just getting stuck in and start coding.

In reality, you have to do a bit of both, of course. You need a good tutorial (I'd say Learning Perl, the perl docs, and online help. Whilst Programming Perl sits open on my desk practically every day, I wouldn't recommend it to beginners) Then get thinking how you can use perl to better solve one or two problems, and see how others did it, too.

Finally, Perlmonks and meeeting other Perl programmers is invaluable for the discussion.