My design process often starts with a sketch or even sometimes a model, I tend to sketch both digitally and on more traditional media with no real preference at this stage. To me the key to the early stages of the design process is just ideation, as much of it as possible.
I often find adding restraints and boundaries helps later on in the process but can hinder creativity. To me there is always a fine balance between designing for manufacture and not hindering the creative process.
After I have settled on a rough form and the key features and functions I begin to work more digitally, sometimes moving very quickly into CAD software. Ultimately I try not to be rigid with my process, to me there is no right way to design, it's a methodology and a game of balance.