Headshots are usually taken for the purpose of self-promotion. It could be a corporate website, your social media profile, dating sites or an actor's portfolio.
Having a “wrong” online presence can become a liability if you are a professional. Some studies suggest that over 90% of recruiters use social media to screen candidates.  And they spend a fifth of their time looking at candidates’ profile photos.
 
Here some tips on how your profile photo should look like:
No sunglasses.
No selfies.
Smile - if your teeth are visible when you smile – even better.
Slightly squint your eyes in a smiling way. Wide-open eyes may suggest fear, or, in extreme cases  even a sociopathic personality.
“Head and shoulders” shot is better than a “face only”.
Dress for the job you want, not for the job you get.
No party or vacation pics.
And keep your head upright and straight (and think positive thoughts which will show on your face). Traditionally, women, in particular, tend to tilt their heads in photos, which can make you look less self-assured.

Remember, it only takes 100 milliseconds for someone to draw conclusions about who you are based on a photo