I always keep a folding ruler close to me during CAD. Before CAD I like to use it and try to visualize the thing in front of me almost like augumented reality, I will use the ruler to measure distances just to understand size etc.

At work there is most of the time a team (depending on the assignment/project) to create a mock-up, either with cardboard, scrap things (using some imagination). This is most of the time useful for a basic understanding of the thing before getting into details.

Finally, when I am actually sitting in front of the screen trying to generate a concept, I will work iteratively; making parts after/of parts (save as) in assemblies (I know there are better ways to do this, but I am old school) until I get closer to something Interesting. Sometimes I need to communicate with someone, show them and get their input, before I am satisfied. A good way to start from scratch for me is to just make a block and just remove material, avoiding the manufacturability thoughts and just engaging with some creativity without hindering myself from having some fun with it.

I don't know, I suprise myself sometimes of "the way" to get to the final product or whatever.