One thing I didn't see mentioned is that people almost always go too hard at the bottom of a hill and wear themselves out by the top. It is deceptive because you want to maintain your speed as the road pitches up and you don't immediately feel the effects of the increased effort. You almost have to go so slow it feels stupid at the bottom and as you continue it will start to feel harder even though you aren't working any harder. That was the first thing I learned when I got my power meter. Pacing even a short climb (~1 minute) so that you can maintain a steady effort to the top and over makes a huge difference.