> When writing a new module, how do you decide whether to write it as an OOP module or a procedural module?

Bod, great to see you thinking about this important topic so early in your programming career!

The most important aspect of any module is not how it implements the facilities it provides, but the way in which it provides those facilities in the first place.

-- Practice No. 1 in Damian Conway's Ten Essential Development Practices

Given its crucial importance, it's well worth spending considerable time studying the dark art of interface design.

My most comprehensive reference on this topic is On Interfaces and APIs. Other useful references:

• Perl Best Practices contains many useful items, such as "Choose object orientation using appropriate criteria" and "Use a hash of named arguments for any subroutine that has more than three parameters" (which works well because humans are better at remembering names than orderings). See also Damian article: Ten Essential Development Practices especially the first item "Design the Module’s Interface First".
• perlmodstyle - Perl module style guide from the official Perl docs
• Writing Solid CPAN Modules

• On Coding Standards and Code Reviews
• Re: I need perl coding standards (Coding Standards References)
• Object-oriented design (wikipedia)

For your question, an outrageously simple answer is to ask: Do I need more than one of these? If the answer is yes, OO is indicated, otherwise procedural.