The first question every new team asks is what a project should represent. There is no universal answer, but there are four patterns that come up again and again. Pick the one that matches how you already talk about your work, and you will spend no time thinking about structure ever again.
By client
One project per customer or account. This is the default for agencies, studios and consultants: everything for a client lives in one place, so when they call you open one thing and see the whole relationship.
It works badly when a single client has several unrelated pieces of work running at once. If you find yourself writing "Acme, website" and "Acme, campaign" in the same name field, split them.
By outcome
One project per thing you are trying to deliver: a launch, a migration, a report. This is the pattern with the clearest finish line, which makes archiving easy and progress obvious.
The tradeoff is volume. Teams who work this way create more projects, so lean on archiving to keep the active list honest.
By quarter
One project per planning period. Useful for teams whose work is a continuous flow rather than a set of deliverables, because it gives that flow an edge: the quarter ends, the project gets archived, and you start clean.
It suits internal teams better than client work, where a customer's timeline rarely respects your calendar.
By owner
One project per person or per small pod. The simplest to set up and the fastest to outgrow: it stops working the moment two people need to collaborate on the same thing, which is usually week three.
Worth using only when the work genuinely is parallel and independent.
Just start
If none of these is obviously right, pick the one closest to how you described your work the last time somebody asked. Renaming a project does not break anything, and archiving is one click, so the cost of changing your mind later is close to zero. The expensive move is not starting.