I’m one of those people who are always working on multiple projects simultaneously. I keep a file folder for each project in the desk drawer to my right where I can access them easily and make notes if someone calls.
That way I eliminate having to file the notes later or having notes written on something like my message pages where they’ll get forgotten the next day. I would suggest having file folders or binders for everything you work on.
You can use different colors for the file folders to make it easier to spot the right one when you need it, it is a great way to enlist your right brain activity as well.
You might also want to consider typing your notes and having them in a Word document for future reference.
I keep a binder with all of the printed out details of each of the projects I have every worked on from golf tournaments, fundraisers, dinners, camping, books and even my travel packing lists.
In the long run, it helps tremendously in saving time to document the information the first time I work on a project and then update it each time I return to do more.