Etiquette or useful guidelines while making video lectures
Do's:


Do your best to pretend there are students in the classroom. Obviously, don't ask questions to the void, but scan the room, move about as you might in a real classroom (but don't go off camera), and take "normal" pauses if you're writing on a board.  This is an example from a short video I made for some of my pre-algebra students, and there weren't any students in the classroom at the time:  http://www.youtube.com/watch?v=est2X6-BVkw
Write big enough and clearly enough so the video picks it up. In the video I linked to, I realized that the pen I was using was pretty crappy, so I switched to a better pen (although I probably should have redone the entire clip). Even better is the way Khan Academy does it, with a digital board that he writes on during the lecture.
Make sure you have a good microphone, preferably one that is wireless that you put on your shirt/lapel. There is nothing worse than trying to watch/listen to a video that has poor sound.


Don'ts:


Don't block the board!
Don't be afraid to make a few mistakes that remain on tape. You can spend too much time re-doing videos for simple mistakes. If you make a mistake and recognize it immediately, fix it as you would in a real classroom. If you find a mistake in post-processing, feel free to overlay the video with a text box that fixes the error -- no one will care. Obviously, you can re-record if you wish, but keep in mind what your time is worth.



  How does one assess how much to explain a topic?


This is one of those times you have to do the best you can and try to elicit feedback from the students after they watch the video. The reason I posted the video I linked above is because I realized that a number of students didn't get it when I first taught the topic.


  In real classroom scenario, it's quite easy to course correct if someone didn't understand the original thought, but in video, you have just one shot. The student either gets it or he doesn't.


Well, that's one difference between face-to-face instruction and online video instruction. This is what email correspondence with the professor is for. You can also consider posting response videos to frequent questions you've been asked via email.