Positioning of wireless router antennas?

Hi everyone,
I currently have the D-Link DIR-655 Router; it’s a wireless N router and comes with three antennas. However, it is too big to fit horizontally on my desk, so I stood it up vertically with the included stand. Does anyone know how to position the three antennas so I can receive maximum coverage at my house? (Mostly on the same floor, would be good if basement has some wireless coverage too)
Thanks!