Lighting
Whether you’re using available light or studio lighting, make sure your space is well lit. If using available lighting, look for the light first and position yourself so that the light is in front of you instead of behind, which will make sure that the light illuminates your face properly (lighting behind you will darken your face in the photo). Find the most even source of light in your home, or go outside if you need to. Even lighting that’s not bright and harsh or too dim or dark will produce the best results.
Space
Make sure that you have ample space above and around you in the frame; this will make sure that you have extra room when you crop the photo. Less distracting or plain backgrounds are ideal, as they allow you to focus on the actual subject of the image: you! The new portrait mode on iPhones 7 and up is ideal for this.
Cropping
If you’re using your phone, you can edit and crop the photo in an app on your phone. If you’re importing it to a computer, you can crop the photo within the desktop photos app or software like Adobe Photoshop.
Additional Resources
For a step-by-step guide on how to take a good headshot with your phone, including good (and bad) examples, go here.