Most accurate technique for taking intraoral radiograph:

Paralleling Technique This is the most accurate technique for taking intraoral radiographs.  The image receptor should be positioned parallel to the long axis of the teeth, while the X-ray beam is directed perpendicular to the image receptor. Ideally, image receptor holders that enable one to aim easily and correctly should be used. This means that the aiming device must firmly grip the image receptor and that there is an extraoral component that allows the X-ray beam to be positioned correctly in both the vertical and horizontal planes.  It can produce either elongation or foreshortening of the image, if the vertical angulation is incorrect or overlapping of proximal surfaces, if the horizontal angulation is incorrect.  McDonald's 10th Ed P:23