Grow a light beard
In a 2013 study from researchers at the University of New South Wales, researchers had 177 heterosexual men and 351 heterosexual women look at images of 10 men in one of four conditions: clean-shaven, light stubble, heavy stubble, or full beard. Participants rated the men pictured on several traits, including attractiveness.
That women said the most attractive beard length was heavy stubble.
"Facial hair correlates not only with maturity and masculinity, but also with dominance and aggression," write authors Barnaby J. Dixson and Robert C. Brooks.
"An intermediate level of beardedness is most attractive," they add.
Build muscle (but not too much)
In a 2007 study from University of California, Los Angeles, 286 women looked at pictures of shirtless men and indicated which ones seemed like they would make the best long- and short-term partners.
Results showed that women were more likely to want short-term relationships with the guys who had big muscles.
The evolutionary signal that might be at work here?
Characteristics like muscularity are "cues of genes that increase offspring viability or reproductive success," say authors David A. Frederick and Martie G. Haselton.
But Frederick and Haselton took away another telling finding: Less-muscular men were thought to be a better fit for long-term relationships. So if you want to catch a woman's eye and hold her attention, you may be better off not going overboard.
One of the best documented findings in psychology is the halo effect, a bias where you unconsciously take one aspect of somebody as a proxy for their overall character. It's why we think beautiful people are good at their jobs, even when they aren't necessarily.
As psychologist and writer Scott Barry Kaufman notes, the halo effect works in other ways too.
In a 2014 Chinese study, more than 100 young people looked at images of men and women's faces and rated them on attractiveness. Each face pictured was paired with a word that described either a positive personality trait - like kindness or honesty - or a negative personality trait, like being evil or mean.
Results showed that the people described with positive traits were rated more attractive.
"Even though beauty is an assessment of fitness value, there is no reason why assessment of fitness needs to be purely physical," Kaufman writes, meaning that acting kind can make you appear more attractive.
A 2010 cross-cultural study - with participants from China, England, Germany, and the US - found that women are most attracted to men wearing red.
In one experiment from the study, 55 female undergrads looked at a color photo of a man in either a red or green shirt, and then rated the man's attractiveness.
Sure enough, the man was rated significantly more attractive when he was wearing a red shirt. The results were similar when researchers compared the red shirt to other color shirts as well.
Interestingly, participants generally weren't aware that the man's clothing color was influencing their perceptions of his attractiveness.