Consider a headset microphone.  I have a microphone on a stand that provides clearer sound than my headset.  However, it was tricky to make sure my mouth was positioned the same distance each time, and volume control in the final product required more editing.

 

Make a full script.   Read it aloud before recording.  This will help cut down on the number of  "uh" and um" sounds.

 

Consider where it will be hosted.  I was able to change the aspect ratio in Captivate so it would accommodate the widescreen block of YouTube.  This option was not seen in Camtasia.