All of the above.
I don't typically dim the room unless it's night time (automatically dimmed) and use a high power LED flashlight that doesn't seal against the egg.
Top, and sides of top will show the air sack. Side of the egg will usually stimulate movement of the embryo and/or show blood veins. Bottom of the egg usually does nothing of interest (for us) unless its a quitter or blood ring. Take your time and be patient.
Admittedly, candling really gave us fits in the beginning also. However, that egg is either going to hatch or not, and you will know for sure at day 18 if it's viable. That's when we candle, and the rest is left to humidity and temp. Light eggs get sent elsewhere, dark eggs go in the hatcher.
Obviously we're hands off hatching and that may not work for most people, but it sure takes a lot of stress out of the process.
Good luck!
