For rock gesture:Clench your fist and hold it in front of the camera with the fist occupying most of the frame and make sure it covers your face for better accuracy

For paper gesture:Hold your outstretched hand in front of the camera with your palm facing towards tha camera and make sure your fingers aren't seperated much for better accuracy

For scissors gesture:Clench your fist and extend your middle and index finger to form a V shape and hold it in front of the camera making sure that your gesture covers most of your face. Also, avoid keeping the index and middle finger very close to each other, in order to achieve better accuracy