If you are happy with your way of storing your files, then this won't help you. If not, you may get an idea or two here.
Although I am explaining the system we used for Dropbox, any Cloud service or network server* will work the same.
We saved almost no paper files, even work-in-progress may have to be referenced from the cloud.
The first level of folders in our system are the main aspects of a design firm:
Administration and Finance folder contents will vary a lot by firm, and aren't very 'busy'. We used separate folders for Sales and Marketing because we eventually realized that they are two entirely different things. Marketing holds all the planning and graphics. Sales holds all the templates for proposals as well as a subfolder for each proposal prepared. These were sorted into WON, LOST and PENDING folders.
Before focusing on Projects, let me say that the Standards folder held all of our Reference files, like codes, our Templates for everything from letterhead to change orders, and Procedures files that explain how to do stuff.
The Projects folder was the most complicated. The graphic above shows the arrangement that every project started out with so that there was some uniformity. The folders at the next lower level tended to adopt the character of the project. So, for instance, there may be a separate folder for zoning and additional folders for phased permit applications.
Of course the actual names are not crucial, just the fact that there is a system and that you can depend on files 'being where they should be'. The names you see here are pretty self-explanatory with the exception of 'backstage', which was our designation for all the stuff that is somewhat private. Backstage was where we kept a copy of the contract, proposal letters, consultants proposals, invoices and accounting reports, fee calculations, etc.
The 'zarchive' folder, so named so it appears last, was where files were moved as they became obsolete. This was not always used, but it gave us a place to put things 'on-the-fly' that had gotten in the way.
When we got somewhere between 10 and 20 items in a folder, confusion set in and we reorganized into a new group of subfolders. The one exception was the dwg files, which remained easy to find regardless of number because our file naming convention for them was ABCD0A201. 'ABCD' was the project ID that was used for everything. '0' was a version ID in case one was needed. 'A201' was the sheet designation. If you are using Revit or ArchiCad or VectorWorks, this is taken care of within the project database.
The beauty of developing and using a system like this is that even years later, you know exactly where to look for a file.
* I think network servers are a millstone around your neck. You buy a server-grade computer, a battery backup, server software, client licenses, a tape or cloud backup system. You pay to have a firewall and a VPN set up. If you did it right, you can access all your files over the internet. If you didn't, oh well.
We used spend over $500 per year having this setup "worked on". For just about the same cost per year, we paid for monthly subscriptions to Dropbox, who in turn buys the servers, battery backups, etc and we get access to all our files wherever there is internet service or 4G/LTE service for our phones/tablets (like on the job site). I will admit that I am oversimplifying, but not much, and not about the costs and aggravation.