The University of Aberdeen study shows that telling the person "I really like you" is likely to push the chosen target to reciprocate the feelings.
It also revealed that if a person shows someone their feelings, through eye contact, smiling - or simply telling them - they are more likely to return the sentiment.
The new study found that 'social cues' - someone's efforts to show how much they like a person - are of great importance in the blossoming of mutual attraction.
"Our latest research highlights how social cues, which signal the extent to which others are attracted to you, also play a crucial role in attraction," the Telegraph quoted psychologist Dr Ben Jones, co-authors of the study, as saying.
A total of 230 men and women took part in the study at the university's Face Research Laboratory.
The researchers showed volunteers four flash cards, picturing a face with different expressions.
The face is shown making eye contact and not smiling; not making eye contact and not smiling; making eye contact and not smiling: and making eye contact and smiling.
"What we found was that the preference for the attractive face was much stronger when people were judging those faces that were looking at them and smiling," Jones said.
According to the study, attractiveness was how someone combined natural beauty and these 'social cues'.
The study, Integrating Facial Attractiveness And Cues Of Social Attractiveness, was published in the journal Psychological Science.