Beccause each learner is different, I'll give only guidelines :

• Teach him the Perl syntax
• Teach him the Perl idioms by asking him to code simple tasks (30 lines max) while you stay by his side and WATCH.
• Show him how to do better (or at least more Perlish)
• Try to spot his weaknesses, and give him the proper advice to correct it
  (some people don't catch recursion, some don't factorized the code, some don't use the appropriate data...)
• Try to spot his strengths, and teach him how to have more fun with Perl by going a little more into the details
• Iterate the previous step letting him handle bigger and bigger code...

But most important for me, is to make him love Perl!
Show him how powerful, easy, FUN Perl can be...

"Only Bad Coders Code Badly In Perl" (OBC2BIP)