It was a challenge for me to understand Grunt, Sass, and GitHub. So I decided to share a starter project I use for each Bootstrap 3 Sass project as well as a video tutorial series to help you learn the workflow..
Sparky: A Bootstrap 3 Sass starter project
I created a starter project that provides a gruntfile with the tasks you need to watch your folder for code changes and then convert Sass to CSS. It also adds any necessary browser prefixes like -moz, and -webkit.
Starting Frontend Sass Development with Node.js, Grunt and Bootstrap 3 (YouTube tutorial)
For those of you who are brand new to Grunt and Node.js projects, I created a 7 part video series showing you how to get setup. I also show you how to test your site locally and with GitHub pages.
Bootstrap 3 Sass Variables Reference
The _variables.scss has a long list variables so I thought it would be helpful to have a printout to read through what is possible to modify in this file.
I hope this helps you avoid some of the frustration and lost time I faced.