Verify your recommended vehicle tire pressure by looking in the vehicles owners manual. (Do not look on the tire, that’s the maximum rated pressure for that tire)
Make sure you use a separate tire pressure gauge. The one attached to the filler hose is usually wrong. Also nobody can “feel” the tires for correct pressure.
Find a filler air hose that is meant for filling car tires.
Fill tires with air, checking with the gauge every 45 seconds of applying air.
When the recommended air pressure is in all of the tires, be sure to replace the valve caps. This keeps dirt and debris fron getting in the valve and opening it cause air to leak out.
Make sure to check the pressure in your tires every 1000k miles, or every other gas fillup.
Proper air pressure ensures the longest life for the tires, and the best MPG for the vehicle.