Conscientious means ‘made or done according to what one knows is right and showing care and precision with painstaking efforts to do something properly: “She was a conscientious worker, always checking her daily work-log before leaving office.”
Conscious means ‘having a feeling or knowledge of one’s own sensations, feelings, etc.; or being aware of one’s external environment’: “Standing in front of the Himalayas, she was conscious of the vast beauty of the place.”
Conscience is the voice some people never hear until they are caught doing something wrong; while truly conscientious people are those whoseconsciences tell them to do the right thing even when they are consciousthat they won’t get caught.