Some idea of just how deep your current CGI or Perl background goes would be of great help. (are you a beginner in both, or already an expert in Perl? It can make a big difference).

Along with the other recommendations, I'd advise becoming intimately familiar with whatever webserver software you might be using, the HTTP RFCs, and if you're going to be presenting results back to the users (which you might not be, in the case of a web service), HTML, XHTML, CSS and WAI.

If you are writing web services, then you'll want to be up on SOAP, XML and WSDL.

Oh -- and if you're going to try to learn by example ... I'd recommend that you don't just go to any random 'script archive' and look at what's available. There is a whole lot of bad code out there, and you don't want to be picking up bad habits from it.