Make sure node and npm are installed. The easiest way is to install node via the available installers: https://nodejs.org/en/download/
Please ensure to use the 4.x LTS version instead of the latest 5.x version. For installing node and npm on debian based distros, these instructions might also work: https://www.digitalocean.com/community/tutorials/how-to-install-node-js-on-an-ubuntu-14-04-server
The easiest way is to use nvm. Simply install it as described here: