I like using a 1 Megameter per millimeter "planets view" (Earth is a blue marble; Jupiter is a striped ball; the Sun is an adult-sized white ball).[1] So you can google for lengths in km, trim 3 digits, and draw in millimeters.
Relatedly, building a scale model solar system, in a hallway, field or neighborhood, is a popular educational activity, with a lot of variants and instructions online.
[1] PDF: http://www.clarifyscience.info/part/RBigE?s=D72k . Broader context: the How to remember sizes section of http://www.clarifyscience.info/part/Atoms (better than the page the PDF is on, FWIW). Two slides (for a 2 meter wide screen): http://www.clarifyscience.info/part/RBigE?s=K2so . Old misc (2001): http://www.vendian.org/howbig/?&page=Megapaper , http://www.vendian.org/howbig/?&page=Megafloor .