Have the camera even with your subject. The photo needs to be straight on, with no angles.
Lift hair away from the back of the neck. A ponytail or hair bun works best. Make sure all of the head and shoulders are included in the photo.
Choose a solid color background, like a white wall. Try to choose something that isn't the same color as your clothes, skin, or hair. The less background clutter, the better.
High Res Photo
Submit the highest resolution photo that you have. Submit multiple photos if you have them.
Submit what you have and your designer will let you know if a different photo is needed.