I guess you have already looked at the documentation for CGI.pm? It is pretty much required reading, I think.

If you are building anything larger than a couple of pages, you might want to become familiar with the MVC (Model/View/Controller) paradigm. CGI::Application, CGI::Builder, Template::Toolkit, HTML::Template, Maypole, Catalyst, and Class::DBI are all useful tools for implementing such a framework (or are frameworks, themselves).