• nodejs (npm) - http://nodejs.org/
• grunt - http://gruntjs.com/
• ruby - https://www.ruby-lang.org/
• sass - https://rubygems.org/gems/sass/

1. Install Ruby.

2. Open "Start Command Prompt with Ruby", them enter the following commands:

   $ gem install sass
   

3. Close "Start Command Prompt with Ruby".

4. Install nodejs.

5. Open "Node.js command prompt", them enter the following commands:

   $ npm install -g grunt-cli
   

6. Close "Node.js command prompt".

1. Open "Node.js command prompt" on project's, them enter the following commands:

   $ npm install
   $ grunt
   

First you need to install the proper node modules using npm install. Then to have grunt start watching for changes, run grunt dev