Before you begin recording, always make sure you've set your resolution to 1280X720. We recommend high DPI, which doubles the pixels just to make it a little bit clearer.
Then make sure that your microphone is coming from your Blackjack rather than any other option. Lastly, make sure that your microphone is being picked up and that it's getting enough volume to get about halfway up, or if you were to cough, it would kick it into the red.
Basically, if I were to talk really, really loud, it would get about three-quarters of the way up, or if I were to cough or something, it would hit the red. Missing any of these three steps -- such as the wrong resolution, or the wrong mic, or the mic being too quiet -- could make your video unusable, so always double-check those settings beforehand.
One tip with ScreenFlow is never use the Record shortcut, because that doesn't bring up this dialogue. It just starts recording right away and it doesn't give you this Select box to select your microphone, in case it's on the wrong one.