There are a few simple things you can do to improve lighting within a webcast. First, make sure that your face is brighter than your background. This can be accomplished by moving your camera position to ensure that any light sources are in front of you. Consider taking advantage of natural light by setting your laptop in front of a window or sitting where the light from a ceiling or floor lamp shines on you.
You can also add more lighting elements such as simple items you can buy online like the Lume Cube Video Conferencing Kit (currently $69.95), the Elgato Key Light (currently $199.99), or hiring a production company to provide you with a video lighting kit. This video lighting kit could be part of a fly pack, a small setup with basic audio, lighting, and video elements meant for recording interviews and small shoots. Three or four-point lighting techniques are standard in interview lighting setups, which you could achieve by purchasing multiple lighting units (like this), hiring a production team, or possibly with lights and windows you have around your house or office.
These points of light are key, fill, hair, and background:
This light creates the subject's main illumination and is usually brighter than any other light on the subject. It is placed in front of the subject about a little off center to one side or the other.
This light helps to eliminate the shadows cast on the face from the key light. The fill light is usually positioned in front of the subject, off center opposite the key light.
This light helps to separate the subject from the background by illuminating the edges of subject. The hair light is positioned behind the subject, opposite the fill light, aimed at the hair and shoulders.
Background (not present in a 3-point setup)
This light's purpose is to illuminate the background behind the subject. The darker this light is, the more dramatic the shot will be.
Of course, any of these are subject to what is available to you. Just like all forms of art, these suggestions are by no means rules that can't be bent or broken. Experiment, get creative, and don't worry if you don't have a full studio-grade lighting rig in your living room. Though this can enhance your shot, it is not always needed. Upgrade with a Studio In A Box. Here are some more advanced tips on a 4-point setup from Arri Lighting.