Sketchbooks are a great place to collect and manage ideas. They are also great to explore techniques and styles. I like to use my sketchbooks to solve problems and take notes and trying out different ideas or just to have fun.
But sketchbooks are not only for sketches. Here I used magazine cutouts to create collages and sometimes I draw on them as well. I like to look at these collected ideas and sketches to get inspired and they are often a great starting point for a new design project.