There’s a quick way to center objects on your page without using the ruler and guides. First you need to select all the objects you want to center. Once you have them selected, Cut them (Command + X). Once you have them Cut to the clipboard, set your view to Fit in Window (Command + 0). And finally, Paste your objects (Command + V). All the objects should be centered on the page. One thing that will make this work as accurately as possible is to make sure that any frames which contain images or text are “trimmed” so that the boxes don’t have excess space to either side.