Pump up the leaky tubes and try to check where the leak is. Maybe put them in water in the sink if you're at home to see if any bubbles appear. Check the valve hole and make sure that there is no rough edge on it. Check the rim tape and replace if it even looks close to being worn. They're only a few bucks so never hurts to replace it. I last bought a plastic rim tape that stretches over the rim and goes on securely. Was only around $4 or $5 at an LBS if I recall. Finally, check the tires. If you see any cuts, then take out the air pressure and pinch the cut to get a better look at it. I sometimes get 1mm or smaller slivers of glass and rock caught in the tire. Just got a front flat from that last Friday. Glad I checked and removed the sliver from the tire...