After you have finished a project, put some effort into archiving it properly. Just because you know now that all final project files are in an obscurely named folder deep down in the folder structure doesn’t mean you will remember that in a year when you possibly need to revisit the project. So make sure to name and sort things properly before you archive them so you have a chance to find a file you might be needing in the future again.
Also, with HDD memory becoming so cheap, you should keep every file of the project. A few years ago, many composers would make a habit of deleting everything apart from the final files of a project before archiving it which might be a good idea in 80% of the cases but there will always be this one time when you need to go back to an old project and pull out an early version or draft.
If you store your archived projects on external HDDs, make sure to lable them properly as well (for example by time period) and also consider mirroring these projects on at least two disks as there are quite a few occurances of HDD’s crashing even if they have been sitting idle in a shelf for years.