Did you know that most drivers lose from 10% to 50% of their car's tire tread life due to poorly maintained air pressure?  Tire disposal is a significant environmental problem.   Another environmental issue is reduced fuel efficiency resulting from the extra energy required for vehicles to travel with under-inflated tires.

You should check tire pressure at least once per month, more often during the summer months when the temperature is hotter.   Always use an accurate air gauge, not those provided at service stations.  They tend to be grossly inaccurate.  Also do not judge air pressure by looking at the tires.

The proper method of checking the air pressure is when the tires are cold.  It is good practice to check first thing in the morning before driving anywhere.  If any of the tires are under-inflated then drive straight to the service station.

If you have to drive your vehicle more than 1 km then the tires are considered "hot". Take another tire pressure measurement with your accurate gauge and note the difference from cold temperature.  Inflate the tire(s) to a level equal to the manufacturer recommended cold temperature plus the difference at high temperature.

Make sure that the tires are equipped with valve caps to keep out moisture.   Moisture will cause air to leak from the tire faster.