Not sure how others go about this but my take is the following.
Idea
This is the launching point. Sometimes this comes from a particular model but it is most likely from a passing idea especially when generated by a conversation with someone. These should always be noted down.  Very often these will go nowhere but the ones that do are most likely to be original. I once had the idea of doing a dio of a missile crashing into the sea near a whale which was based on a news article.  I got as far as buying a plastic whale but no further. I still have the whale, maybe one day it will get used.

Supplies

This is often the point of failure or delay for many projects.  For the one I am currently working on it nearly was. Not being happy with any of the tables on the market including stuff from Verlinden ( which was too old in style ) I had built my own but wasn’t that impressed with the result so just sat on the concept.  Enter Diopark with their work table set and away I went. This looked like something a modeller might use, old and sturdy but definitely someone else’s cast off.
Without enough ready made products to add to my own scratch building efforts this model would not have been started. 
Models within models

On many of these my approach is to try and duplicate real life as much as possible. With some vignettes I have seen like this the modeller forgets basics like lights that have no power cord or an overly clean desk.
An example is the waste paper basket. This has rubbish in it including some screwed up pieces of paper. All have what appears to be writing to add veracity.
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