Ask HN: How do you make a good screencast?

I've been trying to make a good screencast, but since I'm a bit of a perfectionist I'm running into some difficulties. So far I've approached it in two ways:

1) Record the screencast and audio at the same time. This leads to me using a lot of "um"s and "uh"s and seeing lots of little mistakes. It's not the worst thing in the world, but I'd like it to look and sound more polished.

2) Record the screencast first, then go back and script the audio portion. This works a bit better, but I have problems getting everything synced properly.

What are your tips and tricks to making a killer professional screencast?