Swing your arms out into a wide V. Ensure your right hand (the controller hand) reaches the peak of the arc exactly on the beat.
Which are you playing on? (Wii, Switch, Xbox, or PS4?) Are you using a controller, camera, or phone app ? Which specific move is giving you "OK" or "X" ratings? Blue (Da Ba Dee) - Just Dance 2018 (Megastar - *5)
Give a slight "flick" to your wrist at the end of sweeping motions to register a "Perfect." Swing your arms out into a wide V