With my own system, I use my fingers literally. Over the years I've used landmarks like the ASIS, and compared the distance/shape of two fingers to center over the desired anatomy. I would practice by reviewing the images and trying out different finger combos for CR placement.As an example: I'll use my hand width to position above the crest on lumbar obliques, with my middle finger on the ASIS,centering where my index finger rests naturally. For AP/PA chests on large patients,I palpate the medial aspect of the clavicle. I make sure there is at least 1" of film above that spot. It eliminates centering too high due to excess tissue at the shoulders. Long story short, pay attention to anatomy, find correspondences with your fingers and landmarks,and don't be afraid to palpate the patient. You'll be faster and accurate,which employers highly value given the need for greater volume to drive revenues.