You can also place it based on the current viewport - if your layout is really large and you have some scrolling going on, using layoutwidth and layoutheight won't work for placing it in the center of the players screen.
You would need to do something like;
Object.X = (viewportright("layername")-viewportleft("layername"))/2
Object.Y = (viewportbottom("layername")-viewporttop("layername))/2
Of course if your game is just a single screen then what Drasanas said would do the trick.