The apex diagrams provide a pretty good explanation of how to take a line through a curve, and the advice to look somewhat inside your chosen line also good.

Just sticking your outer leg down doesn't do a whole lot...but consciously pushing down with your foot while doing so will add a little more traction, letting you use a bit more body lean without sliding out.

Another thing to practice in diving into and through a curve is exerting downward and upward pressure on your handlebars. You can significantly decrease the radius of your initial turn to dive into a corner by doing so, which moves the "late apex" even later, enabling much faster potential speeds through turns. There's a good explanation of this by Davis Phinney in the book you can download by subscribing to the newsletter at http://www.roadbikerider.com.