I'll make reference to one of my favorite photography instructors online to help answer your question.

The short version is that a rim light is a light source which comes from above and behind an actor or talent which exists to separate them from the backdrop or background. It helps the viewer read the composition of the scene, pulling the speaker away from whatever is going on behind them (even if that's just a solid, motionless space).

You don't ever want to be having flat lighting on you and flat lighting on the background because you effectively disappear, making it much harder for someone to pay attention and stay focused on what you're doing. (This is actually one of the reasons that a lot of online instructors who do three-quarter views end up being less interesting to look at than a close up. The usual composition is widescreen, with a three-quarter view you are taking up only about 1/6 of that screen, and there's just not a lot of detail to notice beyond broad physical gestures. Headshot close-ups at least bring a viewer in on your face and eyes, which gives them something to focus on. Choosing what composition and shot to use at any given moment – that's more an art than a science.)

The easiest lighting in the world to get right is three point lighting, and that's a key light (main light), fill light (a bit of light coming from the opposite side from the main light to make sure that your shadows don't get too harsh; you can use a big piece of white card to balance light from your main if that's what you got), and a rim light to create some contrast between the hairline/profile and the background.

Get that right and you can be visually ahead of 90% of the people doing communication videos on YouTube.

(I have a whole lecture I could give on proper lens selection for various shot types, but no one has time or the sanity points to burn to survive that.)

All that being said, the most important thing to get right for the kinds of videos that you have done is the audio. Clear, crisp, slightly compressed, very slightly noise reduced audio is exactly what your audience wants. Don't record in a room with no sound treatment on the walls because it's immediately obvious when you get that empty room hollow echoing sound, make sure that your mic levels are right and if you have to err, err on the side of having them too low because you can always turn it up a little bit in post if the noise floor is low enough, and don't get overly cute with inserted sound effects or even complicated bed music.

And another of my personal pet peeve, the one almost no one will tell you, don't spend more than five seconds on a title lead in or close out. I've seen so many 15 to 30 second titles and closes that essentially just waste the time of the viewer. Don't do it. It can be really hard to step away and trust that the viewer is there to get just what you're delivering, and so many people can't do that, but it is absolutely crucial. Anything extra that you think people should know, don't stick it in a title, put it in the description. All of that stuff is searchable and clickable, unlike the video.

Oh look, and that's me going off on a long and rambling lecture despite my best intentions.

Hopefully some of this was useful to you. If you have any additional questions, feel free to let me know. Obviously it doesn't take much to get me started talking at ridiculous length.