Right position: hair towards camera in a hair video not face Simple concept but it seems not to be clear at all. Remember: it is a hair video so cover the frame area mostly with wet hair
Hair very saturated and not divided in locks: best when it looks as a unique liquid flow of hair.
White clothes or bathing suits. For the good contrast.
Some good light source pointed towards the hair from the camera point of view so the camera is able to expose the dark areas despite the white background. Notice how glossy in the sample. Nowadays led lights are so cheap that it's worth the extra money for the jump of quality in general for any kind of filming or shooting.
Better to eliminate jewellery and other accessories and clothes that can create tangles.