Wire into your router whenever possible or be close to it.
Limit household use of internet during recording (Netflix streaming in another room may cause your feed to get choppy & freeze periodically).
Avoid connecting with more than one device (Example: Avoid using an iPhone for your webcam, but then watching it on a laptop at the same time.)
If using built in laptop microphone, try to stay within arms length of the computer. Any further away and your audio will suffer exponentially.
Mute your notifications & system sounds on phones and computers.
Avoid listening on a separate system, this can cause an echo even when you're not speaking.
Enviorment / Lighting
Create a stable platform, as slight shaking of a camera can be dramatic to the video.
Use light coming from in front of your face, avoid any bright lights from behind you (If when testing it looks fine, don't worry about it.)
Camera at eye level, and look into the camera.
Sit close enough you're framed like a passport photo.
Film vertical not horizontal when using a smartphone or tablet.