Planning - make a storyboard, practice it a few times. You can either record video+audio live (I do this for simple training material) or record the video with long pauses then do the audio later.
If you do the latter then use e.g. Audacity to record audio and import short segments of audio into CamTasia to sync them with each scene, then cut the long pauses after you've got the raw material together.
Video - I tend to use 800x600 or 1024x768 for recording and transcode down to 640x480 for presentation, with a high bitrate (2000kbps & keyframes every 30 secs) you get crystal-clear video. Expect 2-4mb per minute of video. CamTasia exports with a built-in player so you can easily upload it to the web. I avoid the SWF export and use FLVs.
For audio make sure you've got a quiet room and a nice mic too, drink so you don't dry out. Consider using a lip-salve if you're speaking so much that you get dry (you can hear it in the end result). Get a good mic, a cheap USB will sound...cheap. Decent audio equipment starts at $300US.
For examples of various techniques see ShowMeDo (I'm a co-founder). We have over 700 screencasts by 100 open-src authors, you'll get a good idea of techniques, approaches, voice-styles, editing styles etc.
There are some more tips in this interview I did with Jolt Magazine a few days back including 'stuff to avoid'.
For hosting I tend to host my own (e.g. at my ProCasts), a 3 minute video is about 10mb, any decent ftp host should offer the video reasonably quickly. YouTube has wide exposure but shockingly bad quality. Vimeo looks great and has nice embeddable players.
When hosting my own I use the JW FLV Player rather than CamTasia's default player, it supports nice callbacks (e.g. for start/stop event monitoring) and is skinnable.