Iphones require a lot of light. 

Use smilelite from www.smileline.ch

Ring flash or twin flash for DSLR cameras

Remember the right angulation of your photo

Make sure you capture everything

Video in 5K can be used - frame graps

Retractors should be "invisible"

Keep your mirrors hot (no fog)

Imagine how the picture should look

- .... And take it. 

Good photos require LOTS of practice - keep going. You will improve your skills.