This is a nice site that clearly explains a very reasonable file organisation system.
https://johnnydecimal.com/I'm sure those of us that have worked in any engineering/drafting office of more than 2-5 people have used very similar filing systems but I thought it was a good introduction of how a good filing system works.
I've used slightly different systems but they have all been based on a numbering (alpha-numeric etc) prefix for all folders and files and we could locate a drawing in about 3-5 clicks deep no matter how old the file was.
Example:
Archive->Year->ClientNo-[name]->JobNo->Drawings->[CLIENT:JOBNO] - [Drawing Name] - Rev [A-Z or 0-...].dwg
Current jobs are even easier:
ClientNo-[name]->JobNo->Drawings->[CLIENT:JOBNO] - [Drawing Name] - Rev [A-Z or 0-...].dwg
Locating the job folder is just as easy using the prefix of the drawing/document number, look in [CLIENT] then [JOBNO] then 'Drawings'.
A little bit more on 'project' structures:
https://play.johnnydecimal.com/johnny.decimal/projectsAnyway, thought it might be a good resource for sole trader or smaller offices yet to develop a good system, cheers.