-knees to the top tube (not constantly, necessarily, but think of a tuning fork vibrating -- touch it to stop it from reaching resonance.)
-don't hold the handlebars (the drops) in a deathgrip. Hold them enough to not have them jump out of your hands if you hit an unexpected hop in the road, but dont hold them tightly like a baseball bar or something.
-butt off the saddle. You should be on the pedals with your legs properly extended/bent to handle the tilt/curve of the road coming up to meet you. If it's just going straight down, pick a leg to be in front (like a surfer, you'll figure out your natural 'front' leg') and get your pedals horizontal to the ground. If you're turning right, your left foot should go down (both for balance and to avoid a pedal strike.)
-You want to push weight down through the bike to the road. Your inside handlebar and outside pedal are your surfaces on which to balance when in a turn. Shift between the two most extreme left/right iterations of this, as necessary for the characteristics of the curve you're dealing with.
-Brake before the turn. Use both front and rear brakes. Brake during the turn if you need to, but gently/gradually, not drastically. If you need to take the inside foot out and put it down on the ground to make a tripod of balance out of your wheels and this foot, do it -- the alternative being flying off the road and dying.