Use a tripod.
If you have a cell phone get a cell phone tripod. The reason is so it doesn’t move. When interviewing someone this is a HUGE difference.
Try to avoid moving
When the subject (the person in the video) moves, it can be distracting and it can cut them off.
Pay attention to the background
This is both visual and audible. You’ll notice noise later that you didn’t notice when you were filming. Pets, people, lights, traffic, cups, trash, etc. Try and find someplace private.
Audio
As well as paying attention to the background, if you can, use a lavalier (lapel) microphone. There are some reasonably priced ones that work with your phone.
Lighting
Try to get good lighting facing the subject. Lights in the back of the subject will make the subject dark, and wash out the picture. There is a way to make this work with dimmer lights that are to the side, but don’t worry about that. If you put something like a window on a sunny day, it will be awful. When outside, try to put the sun either behind you or to the side.
Framing
Think about what is will look like before you start filming. A lot of people frame it in portrait mode- similar to tiktok. Please do not do this. Use landscape mode. There will be wasted space, but the subject of the video won’t have anything cut off.