1) Back off the mic and project your voice
This avoids audible breaths and you will have a better quality of voice.
2) Use consistent mic placement
This maintains the same level of ambience.
3) Listen for noise
Buzzing or other noise will lead to a bad mic connection.
4) Trim heads and tails of audio clips
This will remove the start and stop "pops" and improves pacing.
5) Use a pop filter
This avoids "popped" P and B sounds.
6) Normalize audio clips
You can use Audacity, a free outside program to create a consistent volume throughout your clips.