Try ‘Metro map creator’ as a step by step visualiser.
Go to http://beno.org.uk/metromapcreator/ to create your diagram.
Essentially designed to create tube/train line diagrams, this can be easily adjusted to create step by step guides.
You can create different colour lines and add marker/milestone points along the line. You can add new ‘stations’ which allows you to add text to the diagram. The site can be a little fiddly and requires you do things in a certain order, however once you get used to it you’ll be able to create some great diagrams. Once completed you can download the image in high/low res.
(Screenshot from metro map creator)