rsbob 

Good advice above.

in addition, Remove the tube and keep it in the same position as it came out of the tire. Inflate the tube and listen for a leak or slowly move your hand over the tube feeling for escaping air. If you find the leak, look at the exterior of the tire for the culprit and gently sweep your fingers inside the tire casing for anything sharp. If you cant find the leak, submerse the inflated tube and look for bubbles and patch there. Or save yourself a lot of time and sweep the inside of the tire, remove the culprit and put in a new tube.

be sure that you are not running your tires under inflated. Check the max pressure on the tire casing and lower it by 10 lbs.