Check tire pressure and tread monthly using your door-jamb label
Added
Once a month, with the tires cold (not driven for at least 3 hours), check every tire including the spare against the pressure on the driver's door-jamb label or owner's manual, not the number on the tire. Check tread at the same time with the built-in wear bars or the penny test. Useful for anyone, and especially if you drive rideshare.
The result
Result: NHTSA: replace tires when tread is worn to 2/32 inch, and a dashboard TPMS warning only comes on when a tire is already significantly underinflated. NHTSA says proper inflation can save as much as 11 cents per gallon on fuel.
Source
NHTSA TireWise (opens the original source in a new tab). Check it for the latest numbers before you act.