It's quite complex. It can't be stated briefly. There are many distances, ratios and individual features to consider if you want a full answer to this.
To simplify it...
1. FACE SHAPE - Yes, basically strong cheekbones and jaw and the RELATION between these two. Cheekbones are more important. You must also consider the temples and cheeks. Light bulb shaped heads are very unattractive. Chubby cheeks are unattractive.
2. EYE AREA - The lower eyelid should be straight for men. Positive canthal tilt. Strong brow ridge which creates hooding of the upper eyelid over the eyes and low set eyebrows.
3. Skin, hair, etc.
Believe me, face shape and eye area are the two most elemental things. Address these first and foremost.