When taking an avatar, you should not only take some lively personality expressions. A more formal photo similar to the ID photo style is definitely essential. On the one hand, taking this photo can turn on some built-in grid functions of the camera and make it horizontal and vertical, which makes it look more formal.
You can adjust the horizontal line of glasses, the horizontal line of ears and the mouth and nose as reference objects. Moreover, when shooting, you can enlarge the frame as much as possible and leave more background to leave more space for post-processing.
If it is a fully automatic digital camera, you can use the portrait mode that is usually preset inside the camera. In this way, the camera will give a shooting parameter suitable for portrait shooting according to the original preset, so the portrait will be better.