I'm a little confused with the rule of thirds. I know that you should imagine a grid somewhat like tic-tac-toe and place the subject on one of the crossing lines. My problem lies with setting it up. Do I focus on the item that I'd like to have as my subject by using the center dot in the viewfinder (lock the focus or hold button) and then shift away from subject, placing it at one of the imagined cross lines? I hope this makes sense.