A project never starts without a pen and paper close to hand. A whiteboard will also do. My first action when getting into something new, whether it involves an entirely new concept or a modification to an existing system, is to scribble my way through reams of paper. The shared creative process of pen on paper offers so much more collaborative benefits than going straight to a screen.
The main wireframing tool I have experience with is Balsamiq. Building up wireframes is often a very valuable step that I find particularly useful in building consensus about a project before moving along to mockups or code. Sometimes pen and paper will suffice but the ability to build some level of interaction into a wireframe can be a huge benefit.