Microphones are essential for good quality video production. Improving the audio recording quality comes down to capturing all the sound you want, and none of the sound you don't. Adding a microphone to the camera is an instant upgrade, as the built in microphones are typically very small and limited. A higher quality microphone will capture a clearer recording. A directional microphone, such as a shotgun mic will reduce ambient noise, and only record more of the what your subject is saying.