You can easily align table centres to a grid by turning on grid snap.
You can move selected tables using the mouse or keyboard arrow keys. If you press an arrow key when grid snap is on, the item will be moved one grid position. If you press an arrow key when grid snap is not on, the item will be moved 5 cm/2 inches (1 cm/0.4 inch if the 
key is held down).
If you depress the 
button at the top of the Floor plan pane, guides lines will be drawn when you move a single floor plan item.
See also: