Match the background to the job of the video. A talking-head explanation usually needs something clean and low-distraction. A social ad can use faster motion, bigger typography, and stronger color. A product demo should keep attention on the product, not the background.
Also check resolution and framing. For vertical clips, pick vertical or crop-safe backgrounds. For horizontal YouTube videos, choose 16:9 backgrounds with enough empty space around the subject for text.
Finally, keep the lighting believable. A subject shot under cool office lighting will look strange on a warm sunset beach unless you color-correct the clip or pick a more neutral background.