If you're not using a responsive framework to develop websites you should seriously consider changing course this year. Using a pre-built framework can save you time, help you avoid errors, and lead to a more thorough and better developed site.
ZURB has been designing products since 1998 and Foundation is their answer to advanced responsive front-end development. It's easy to learn and quick to grasp. We use this framework for the bulk of our client projects.
Skeleton is about as simple as it gets. It is a bare bones responsive framework intended for smaller projects or for those that want a non-stuffy starting point. I've used this on a handful of sites - mostly where I'm creating a simple website with only a handful of pages.
There are many other responsive frameworks from which to choose. These are just the three that we have used and recommend. They're worth taking a little time to learn because each can have a nice cozy place in your web development arsenal.