Cook asked 45 people to face off against each other in several rounds of rock-paper-scissors, in exchange for real money. In every game, either one or both players were blindfolded.
Cook found that the players drew with each other more often when one of them could see (36.3% of the matches) than when both were blindfolded (33.3% of them). The latter figure was exactly the proportion of draws you’d expect if the players were choosing randomly; the former was significantly higher than chance.
Cook devised this study because he was interested in the idea that we all automatically and unconsciously imitate one another. There’s plenty of evidence that we do indeed copy one another, from obvious gestures like touching our face to subtle movements like tensing our muscles. But it’s not clear whether these actions are truly involuntary in the way that the knee-jerk reflex is. To find out, Cook wanted to see if people can stop themselves from performing these acts of mimicry.
That’s why he turned to rock-paper-scissors. Here is a game where you have to avoid imitating your opponent in order to win – the rules implicitly encourage people to avoid copying what their adversaries do. The results of Cook’s face-offs suggest that the sighted player has a slight tendency to imitate the blindfolded one – that’s why a blindfolded player will draw more often against a sighted one than another blindfolded opponent. And indeed, players were particularly likely to imitate rocks and scissors.
If that's not an option in your game, Ed Yong offers a list of tips for a beginning player. Link