Currently I'm recording long dull screencasts for proof of concept, not for education or entertainment. Documentation is a better medium for education. Short-form edited video is better for entertainment.
Below are some notes on my screencasting methodology. It's nothing special, except perhaps exceptionally low-effort.
Ambient noise adds no info value. The best way to remove it is to never record it.
Muting is best done at the software level to avoid feedback. For MacOS, Mutify works.
Unfortunately Mutify caused electet mic pop with the directional mic I switched to, so I discontinued use. A better mic would fix.
If your mouth stays in the same location during recording, a directional mic is a great means of reducing ambient noise.
In combination with Camtasia's noise filter, I get acceptable results with this method, for current quality needs.
What is the best positioning for a headphone mic? The bendy wire can hold it at the throat, away from the face, in front of the mouth, etc.
This is just my opinion based on a little casual experimentation. I think the richest sound comes from placing the mic by the forehead. That takes advantage of the resonant sinus chambers, which make the voice pleasant. It's also well away from smacky lips and breathy airstream.
Looks funny on camera, so that's why it isn't done, I assume. Also has trouble competing with ambient volume.
Speed up the clip, since watching is easier than doing.
Lower vocal pitch, since that's more pleasant and authoritative.
Noise filter, default settings.