|No such thing as a small change|
Write Code. Write code that you actually use. Write code that scratches your own itches.
Find some small repetitive task that you often perform, and make your life easier by doing it in Perl.
Seriously, there's nothing better for learning programming than programming.
When you write code, you learn the things that actually matter for you, not the things that some book author thought that matter for you.
If you misunderstood something, your code won't work, and you have to investigate. If you misunderstood something in the book, you will memorize it the way you wrongly understood upon rereading.
If you write code, you will also find that some things are just cumbersome to do, and you will appreciate things like reference once you read about them in the more advanced books, because they will actually make your life easier.
Write code. Write code you use. Write code.