Clean up the background
Use as neutral of a background as possible, which will reduce the potential for distractions. For example, a plain wall or a closet door is typically preferable to a wall plastered with posters. You should take care to reduce background noise as well as potential interference with the recording from fans or other moving objects. Don’t forget to hang a sign on your door asking not to be disturbed!
Consider your clothing
Just as you want to reduce distractions from your physical space, your clothing should be appropriate for the speaking occasion and for the camera. Shirts with stripes or busy designs may be distracting on the camera. When in doubt, simple designs or solid colors are preferable. Generally, avoid a baseball cap or other brimmed hat as they create shadows.
Position yourself for success
Cameras should be positioned so that the audience can see from approximately your navel to the top of your head. Your head should be in the top third of the screen. The camera itself should be positioned at approximately your eye level so that you are not distorted and the audience isn’t looking up your nose. You may need to stack some books to raise your laptop up to a better height. You can find more examples of framing a video here. Some people are more comfortable sitting for a video presentation, though standing tends to be better for the voice. If you are seated, be aware of inadvertent movement from rolling/spinning chairs.
Pay attention to your nonverbals
Look into the camera, not at the screen. Looking into the camera will create the appearance that you are looking at your audience. Keep in mind that gestures may be less visible than in person and so you should take care to gesture such that the audience can see.
Make some tech tweaks
If you have an external microphone, use it. Either way, make sure you check your input volume before you record, including checking it from wherever you plan to stand or sit. You should be well lit so the quality of your video is not degraded. At minimum, make sure you do not have a significant light source behind you (e.g., your back to a window which makes you into just a silhouette). If you can put a light above and behind your web camera, it will cast light on your face without introducing substantial shadows and be a useful supplement to overhead lighting.