I particularly agree with toma's comments above about the API. Once you know how to 'do' Perl OO, the hard part is designing the API.
My advice is to learn the basics of Perl OO, firstly from the docs perlboot, perltoot, perltooc, perlbot. I also found this book by TheDamian very good.

Then I suggest you try out using the techniques in a few small projects. I know this goes against normal guidelines of when to use OO, but I think it's important to be able to experiment and not have to worry about making mistakes.
I think spending time designing the API before coding is vital, as there's nothing worse that working on a large project and having to make changes throughout when you realise the API is flawed.
Once you've go the API down, then you should be able to make changes to the object structure without having to change everything that uses it. It rewarding when you can do that and you know it's because you've got a good design.