Navigate to the root of your theme in Terminal.
1. Installing grunt globally
npm install -g grunt-cli
I ended up preceding this with sudo to get it working.
2. Move Gemfile, Gruntfile.js and package.json to your theme's root
3. Install gulp (globally) and gulp-cssimports
`npm install gulp
npm install gulp-cssimport``
**4. Install required packages**
`npm install`
**5. Run bundle install**
`bundle install`
**6. Run grunt**
`grunt`