Headset microphones are used by many screencasters. They produce acceptable sound at a reasonable price – particularly USB microphones like the Jabra GN2000 USB Headset – and they leave your hands free for keyboarding. Unfortunately, you can often tell when a screencaster is wearing a headset by the background sounds.
Most people’s first instinct is to speak directly into the mic by placing it in front of the mouth. This results in the mic picking up breathing sounds and popping on letters like “p” and “b”. The correct position for the microphone is counter-intuitive. It should be beside or below your mouth – where it will be less likely to pick up exhalations.
They also offer this advice on microphone type and placement:
The proper positioning of the microphone arm and boom is important in order to ensure a clear, consistent vocal delivery. The optimal placement of the mic is usually 1-2″ from the corner of the mouth. Positioning the mic directly in front of the mouth is not advisable, as plosive distortion and exaggerated bass response (called the proximity effect) will undoubtedly occur. We recommend using omnidirectional polar pattern head-worns for most applications. They are easy to use and provide excellent quality audio We have found that omni mics offered a surprising amount of ambient isolation, probably because of the close proximity of the mic to its source and the small size of the capsule. Omni’s tend to be much more forgiving off-axis in terms of signal pickup and exhibit little or no proximity effect compared to cardioids. Directional polar patterns are sometimes better suited for situations where there are loud monitors, extreme feedback or environmental noise.