I like to use my sketchbook as a source of ideas for my paintings. Over the years I have sketched and kept visual diaries of things and places I have seen. These help to bring up memories of place. I can move things around or change colours or just get some compositional ideas from my quickly jotted down ideas whilst on the move so I can work on them later whilst in the studio. Even the simplest of sketches can provide some idea of what you might do.