I've had my ZZ plant for about eight months now and it's honestly the easiest thing I own

I've had my ZZ plant for about eight months now and it's honestly the easiest thing I own. I barely water it and it just keeps growing those glossy leaflets. My only question is—how do I know when it actually needs water? I wait until the soil feels completely dry, but I'm worried I'm either overdoing it or missing something. Also, does anyone else's ZZ get that dusty film on the leaves, or is it just my Mediterranean heat doing that? Would love to know what actually works for cleaning them without damaging anything.