Make sure you don't exceed the max pressure rating of your tires. Some might tolerate it better than others, but we blew up 2 tires on the highway at 70+ mph because they were 10 psi over their max. Turns out we had a tire gauge that read 10 psi off.
As implied above, we run all our tires at their max rated psi. Not the best ride, but they tend to get good mileage, and since we almost always carry a load, they wear pretty well too. If you want a better ride and better traction, turn the pressure down until they barely start looking "low".