Maintaining the proper tire pressure in your tires is crucial to your safety and essential to the overall tire performance of your vehicle. 

Here are some points you should follow:

1) Use a proper tire pressure guage to measure the tire pressure. 
2) Check pressure and inflate when the tires are cold. (A hot tire will show inaccurate reading due to heat expansion) 
3) It takes as long as 4 hours for a tire to cool down. It¹s a good idea to check the tire pressure first thing in the morning.
4) Don't forget to inflate your spare tire too! 
5) The correct air pressure is shown on the tire placard (or sticker) attached to the vehicle door edge, door post, glove box door or fuel door. If your vehicle doesn't have a placard, check the owner's manual or consult with the vehicle manufacturer or your local tire dealer for the proper inflation.