New drone pilot here. What's your reasoning for saying to always fly it in manual mode?
I'll take a shot at that question if you don't mind. The basic answer is to keep a consistent brightness in the recording.
The built in light meter is designed to keep a certain 'overall' brightness in the scene.
Let's say you're flying down a road and the camera is pointed to the ground or trees for example.
If you then aim towards a bright sky the meter will change everything to darker because now the bright sky is taking up a lot of your image and the meter is adjusting to it.
If you see some of the same trees in the same frame with the sky
they will now be darker also and it just gets to look bad after a while because the brightness is all over the place.
If you're flying in manual mode as JA suggests the scene will have a nice constant overall brightness.
There are exceptions to the rules of course.
You do need to figure out what the important parts of your video are and set your exposure to those readings. One way is to point the MP towards whatever is important, if possible, change to manual mode using those settings.
Once again there are exceptions and it's hard to cover exceptions here.
You might want to read up on photo exposure.
Exposure of your video is controlled by ISO, Shutter Speed, Filters-if any, and aperture. If you change any one of those you need to change something in the other(s) to keep the same exposure. I think the aperture is fixed on the MP so you don't need to worry about it.
Hope this helps and isn't way more than you wanted to know....