Distance Matters More Than You'd Expect
Holding a phone at arm's length, the closest comfortable distance for most people, puts the camera close enough to introduce noticeable distortion, especially on wide-angle front cameras: the nose and forehead can appear slightly enlarged compared to the rest of the face. Where possible, prop the phone up further away and use the timer or a remote shutter instead of holding it close.
Use the Rear Camera if You Can
Front-facing selfie cameras are often lower resolution and more wide-angle than the rear camera on the same phone. If you can set up a timer shot or have someone else take the photo using the rear camera, you'll usually end up with a sharper, less distorted result, which matters more once you're cropping in tightly for a circular avatar.
Face a Light Source, Don't Stand With Your Back to One
The most common selfie lighting mistake is standing with a bright window or light behind you, which leaves your face in shadow while the background is overexposed. Turn around so the light source is in front of you or to the side instead.
Hold the Phone Slightly Above Eye Level
A phone held below eye level tends to produce an unflattering upward angle. Raising it to slightly above eye level and tilting it down a little generally produces a more natural, balanced look, and gives you a frame that centers more easily once cropped into a circle.
Leave Room to Crop
Just like with a proper headshot, frame the selfie a little wider than you think you need. That extra space around your face and shoulders gives you room to reposition and center the shot precisely during the circle crop step, rather than being stuck with whatever the original framing happened to capture.