Have a look at the book "Perl Best Practices" and check out the module Perl::Critic which checks your code against the suggestions in the book.

Perl::Critic let me know I was using a lot of "unless" statements for comparisons where "if" statements would work with the '<' and '>' swapped. It made my program easier for others to follow.

The non-free version of ActiveState Perl comes with a Perl Critic graphical application or ebook that lists the rules and is good reading. But I haven't been able to find a free version of that.