The drawing can only be resemble to one of the faces in the photos. So, with smiling is great! You can upload multiple photos, it helps us to choose the best face angle and expression for your artwork.
Please make sure photos are clear. No blurring. In addition, the lighting doesn't obscure any facial features. Avoid mobile phone photo or those taken from Facebook album if possible. Most of these produce poor results.
Front shot or 1/3 turn view. Avoid photos taken from above the person's face, because it changes the face shape and decrease the face likeness.
The face size need to be larger than the boy's in the following photo.