Here's some information about using Razor with Amavis and SpamAssassin that I collected in the process of getting stuff working.

 * Install Razor
If you are using Debian there is a package for Razor.  There are probably RPMs out there also.  You could install things by downloading, untar'ing, and Make'ing.  But Why? :) 
   Do this as root:  "apt-get install razor"
   
   After saying yes to downloading the dependencies and installing you have to some other steps.  These are much like the RazorSiteWide steps, but specialized for Amavis.

 * Configure Razor

Do these things as root and substitute the right directory and user names.
         - You will substitute {amavis-home} for the diretory specified in your /etc/amavis/amavisd.conf file.  Here's the variable: $MYHOME = '/var/lib/amavis'
         
         - You will substitute {user} and {group} for the user and group specificed in your /etc/amavis/amavisd.conf file.
                   The variables are:  $daemon_user  = 'amavis';  $daemon_group = 'amavis';  

         - "razor-client"

         - "razor-admin -home={amavis-home}/.razor -create"

         - "razor-admin -home={amavis-home}/.razor -discover"
         
         - "razor-admin -home=/var/lib/amavis/.razor -register -user postmaster@yourdomain.org"  # Note I have filled in the directory here as an example.  Substitute yours.
         
         - "cd /var/lib/amavis"
         
         - "chown {user}:{group}  .razor"
         
          - "chown amavis:amavis  .razor/*" # Note I have filled in the user and group here as an example.  Substitute yours.

    EXPLANATION:
         - IF Amavisd-new daemon runs as the user/group "amavis" and /etc/passwd has "/var/lib/amavis" as it's home directory (which you should do when using adduser)
            THEN the environment variable HOME will equal "/var/lib/amavis" when Amavisd launches SpamAssassin and also when SpamAssassin then launches Razor.
                
        - SO, since SpamAssassin is looking for its configuration/home in /var/lib/amavis/.spamassasin and Razor is looking for its home in /var/lib/amavis/.razor, everything thing is wonderful.
 
        - To check things out do a "razor-check -d" (for debug) and look how and what it discovers.

* Turn on Razor in SpamAssassin

   - Edit your "/etc/mail/spamassassin/local.cf"
   - Change the "use_razor2 0" line to "use_razor2 1"

* Restart Things