Well, cover the basics first: statements, variable types, constructs, operators, functions, file handling, regular expressions, subroutines, modules. Of course, references, hashes and objects are part of these basics.
Next on my list of important things is general knowledge of programming. I know many people advise to learn programming in a structured way with another programming language than Perl, like C. Perl has a very easy learning curve, for starting programmers. After the basics, the learning curve becomes more steep. But still, it's possible to do this with Perl. Just keep in mind that you have to be able to read your own program after a year. Better still, imagine that you have to write a program that has to be maintained by a murderous psychopath with a big axe, who will not be happy when he cannot understand the code. When you learn programming in Perl, read many examples and books, see how things are done there. Make your code a pleasure to read, it must be a joy to see you code, and no murderous axe-man will come after you.
As important is documenting your code. Try to be a teacher with a very difficult and rough class. It should be fun to read your documentation. After a year, you should be able to understand your own code by just reading the documentation.
Of course, all of this goes for programming in any language.