Creating a responsive DNN skin requires some upfront planning. Based on the complexity of your site’s design, this could be just a simple wireframe, or full design comps for mobile, tablet portrait and tablet landscape. As a matter of fact, if you are starting with a fresh design, it would be a good idea to think about designing your site with a mobile first design approach. If this doesn’t sound like fun to your graphic designer, I don’t think starting in Photoshop with mobile is required. I would start the wireframe process with mobile first, then start moving up in device size. This way the important content is thought of at the beginning and the mobile user won’t be treated like a 2nd class citizen.
Once you have your design, it’s time to start skinning!