Extend both arms in front of you and make a small triangle with your thumbs and index fingers
Center a distant object in the triangle
Keep both eyes open and slowly bring the triangle toward your face
The eye that keeps the object centered is your dominant eye
Another method: point at a distant object with both eyes open
Close one eye, then the other
The eye that keeps your finger aligned with the object is your dominant eye
Another method: look through a small opening made with your hands or a card
Close each eye one at a time
The eye that still sees the target centered is your dominant eye