There are two key parts to creating a good video: good audio and a good visual. Low-quality audio is often much worse than a bad visual.
For good audio:
Speak up in a quiet room. This will make sure that the white noise is not normalized with your voice.
Use the microphone on your earbuds instead of the one in your computer or phone. This allows the microphone to be closer to your mouth and creates a better recording of your voice.
For a good video:
Do your best to keep the recording device steady, whether it is on a tripod or just resting on a desk.
If you are using a smartphone to record your video, take a horizontal video.
Try to keep the microphone hidden from the camera.
Some information for this section was gathered from this video.