Just go out one day to a local trail, bring a floor pump and tire guage and play around with diff. pressures. Start with say 45 or so, do a quick run then drop it 2 psi. Because you are a light rider you may not notice any chage until you get down to around 34 but give it a shot and see what pressure you like the best.
That's definitely worth the time. I have experiemented with different tire pressure lately during rides and have noticed a big difference in rolling resistance v. traction. Finding your ideal tire pressure based on rider weight and trail conditions can make a huge difference in how your bike rides and how much fun you have.
-Moab