The breath, when you’re at rest, and not intentionally practicing a specific type of breath-work, should be relaxed, effortless, easy, slow, nasal, and diaphragmatic.
It should not be shallow, through the chest or mouth, rushed, forceful, or tight.
A pace of 10 to 12 respiration cycles per minute (1 cycle = 1 inhale + 1 exhale) is good; less would be even better, but higher is where you don’t want to be.
If you haven’t recently paid conscious attention to your breath, just remember:
You have a finite number of total breaths that you can actually take, in your lifetime.
Less is more.