Purpose of your headshot

Friendliness / approachability-

If the headshot is correctly composed, the face is the main focal point, so expression counts. It should not be overly animated, unless for an entertainer perhaps, but I'm speaking mainly about business headshots. Looking friendly and approachable is important, and eyes having good engagement with the audience. No one will have success with a photograph that ha an expression like they swallowed a holly bush.

Confidence -

Especially for young professionals, showing confidence without looking smug will stand out better to employers, freelance or independent. Posture, body language, and expression are all key players here.

Wardrobe -

Always be well groomed and dress the part. Coordinating setting or background is an important task for the headshot photographer to make sure all is coordinated properly. (That is why I went with a gray background for the fellow in the white shirt.)

Effort-

The fact that you went the extra mile and bothered to invest in a professional headshot shows you're serious, and invested in the process. It shows a level of care and responsibility. All positive things in the workforce, for the employee or entrepreneur.