Draw a line all the way across the tire with a white crayon. Drive down a smooth flat road for a couple of miles. Get out and look at the line. When the line is wearing evenly across the whole tire your at your approximate optimum air pressure for tire wear.
If you go any higher you will get a rougher ride, better steering response, wear out the center of the tire faster and get better gas mileage...if you go any lower you will get a smoother ride, mushier ride (less steering response), wear out the edge of your tire faster and get worse gas mileage.
It may take some time to do it this way but then you will know. From the factory they take a lot of variables into account, steering responsiveness, tire wear out, gas mileage, etc. when setting the recommended pressure.
You obviously give some things up and get some things when you raise and lower the pressure. The 37" tires on my 4 dr JK are set at 24 psi after doing the test. They are wearing evenly across after 15,000 miles but I'm sure I could get better mileage if I bumped it up.
I am not an expert in this area (I sold tires for 9 years and am a mechanical engineer so I consider myself at least knowledgeable :-) but have found this method to work quite well through the years and do it on every new vehicle I purchase and every time I buy new tires for a vehicle (all tires are different).