Can someone tell me what's the proper way to layout a toilet flange? I know it needs to be squared up with the back wall but exactly how is the proper way to do it?

Your flange needs to be 15" away from side walls and 12" out from the back wall to the center of the flange hole. Your flange has two elongated slotes for the mounting bolts and the slots are larger at one end so you can insert the bolts after the flange is screwed to the floor. Rotate the flange so that the small end of the slots line up with each other and form a line perfectly paralelle to the wall.