Installing Ghost in Plesk 12 panel is easy, just install JXcore Plesk for Node extension and ready.

1) Install JXcore Plesk for Node from menu: Extensions > Extensions Catalogs > Install JXcore Plesk for Node

2) Click JXcore Plesk for Node and activate the option "Allow user to install NPM module" and clik OK:

3) Copy Ghost files to root of web folder: /var/www/ or some other folder you defined for root of web files.

4) Write NODE_ENV=production in "Environment variables":

5) Finish, Ghost now active with Plesk panel.

Update: JXcore extension in Plesk has been deprecated and no longer available. Plesk provides new extension for Nodejs and Docker.

I wrote update: "How to Install Ghost with Node.js Extension in Plesk Onyx".