If you take a look inside a sketchbook of a designer, you can see the creation of their ideas: everything from branding to illustrations and headlines for corporate communications, beginning life as scamps and doodles.
This is the most invaluable tool for any designer. The sketchbook is a test bed and journal, and best friend if utilized to its potential as an extension of the designer.
Here are a few tips:
Take it everywhere! You never know when something might deserve remembrance in your sketchbook. Additionally, if a potential employer happens to notice, you will always have something to show.
Include a lot of writing and annotations.
Treat it like a work of Art. Employers will look at your sketchbook like a resume and portfolio. Treating it with the same care as you do your finished works will add to your professionalism.
Collect in the name of sketching! Certain items such as stamps, tags and reciepts might give you inspiration.