Wherever you film keep the strongest light source behind you so that it illumines the scenery or the interviewee’s face. To fill shadows in dark areas of your photo or video, you can use an ordinary photography reflector to ‘bounce’ light from the primary light source into areas of the shot that are in shadow.
You may also choose to use an external light. Some tripod mounts, like the Sevenoak SK-PSC1, have a cold-shoe mount to attach a portable light – and popular cold-shoe lights include selfie ring lights, Lume Cube and lights by Manfrotto and iBlazr.
If your external light is too bright or harsh when pointed directly at your interviewee, consider ‘bouncing’ it off a wall or ceiling instead. Many external lights also come with coloured filters that produce a colour temperature that is closer to natural light.
You can also use a standard photography soft-box light. These are low cost and are usually lightweight. If you haven’t got an external light, some apps, like Filmic Pro, allow you to use the phone’s flash as an extra light source.
This tutorial from CNet Australia is a couple years old now so the equipment recommendations aren’t up to date, but their advice on working with indoor and outdoor lighting is excellent if you’re new to video storytelling.
The BBC Academy has also published excellent tips on using external lights for TV journalism, and much of this advice applies equally to mobile journalism.