Refer to your vehicle's owners manual for the proper level of inlation; it may also be postedon the door post or in the glove box.

When you check the inflation pressure, make sure the tires are cool - meaning they are not hot from driving even a mile. 

NOTE: If you have to drive a distance to get air, check and record the tire pressure first and add the appropriate inflation pressure when you get to the pump.  It is normal for tires to heat up and the inflation pressure inside to increase as you drive.  Never "bleed" or reduce inflation pressure when tires are hot.

Remove the cap form the tire valve, firmly press a tire gauge onto the valve and note the reading.  Add air to achieve recommended inflation pressure. 

If you overfill the tire, including the spare (NOTE: Some spare tires require higher inflation pressure.)