Finding the Bottom of Your Phone
To ensure you are recording right-side up in Landscape, the record button should be on your right or on the side that your charging port is located.
Nothing ruins great footage like having two black vertical bars along both sides of your video. To avoid this amateur mistake, make sure to use landscape orientation and not portrait orientation while recording.
Not only does landscape make your video seem more aesthetically pleasing in general, it'll also make it more enjoyable to watch when viewed on a widescreen or television. Plus, you'll capture more in the actual video.
So just remember: Never hold your phone vertically while recording, unless you really like or want those vertical black bars included (or if you're recording purely for Instagram Stories).
Now that you're recording in the proper orientation (see above), completely fill the frame with your subject. You can also put him or her or it slightly off-center to create a more visually interesting scene. Just play around and see what looks best.