Get some shoe polish and stripe it from the sidewall down onto the tread. Adjust pressures until when you run hard you wear it evenly off the tread but not off the sidewall. I've always done it this way on my autoX and track cars and its worked really well. For a generic recommendation I usually end up at about 42psi front and 38psi rear for lower profile tires on heavyish front engine rear wheel drive cars.

Obviously for significant street miles you might want to go with a lower pressure and then just increase it for the track/autoX. This is what I do and I generally run 32 to 36 on the street depending on the car and tire.

-Jon