Apart from looking at how others do it and what you like there: Draw a full head to shoulders, cut out the panel shape (or many shapes) from a different sheet and play around. Or you take a head photo shot and play around with crops in photoshop. That should give you an idea of what you like. It will probably depend on the focal point of your storytelling (creased forehead, shocked eyes, wrinkled nose, clenched teeth, all of those) And when it comes to panel arrangements: Check, if any line, that gets cut off by a panel border, is picked up at the next panels border. If so, it might connect the images in an unwanted way. That problem is not exclusive to head and body crops, it can happen with any line.