Sitcom is primarily about character, but of course the situation matters, too.
So, what makes a good situation?
A contained world
You need a contained world that keeps your characters together and facilitates their comic interactions.
Perhaps this world is work-place, perhaps it's domestic.
If you're writing a workplace sitcom, then the situation is the workplace, and the locations might be the "shop floor" or office, the manager's office, and a small coffee bar or place-where-the-staff-hang-out.
Similarly, the simplest domestic sitcom might take place across a larger kitchen/sitting room set, and a couple of bedrooms.
Ideally, your characters will also...