Cisco Access Points usually ship with mounting hardware for a recessed ceiling (drop ceiling with recessed tiles). Detailed mounting instructions are posted at http://www.cisco.com/en/US/docs/wireless/access_point/mounting/guide/apmount.html
A direct quote about Cisco recommended mounting: “Access points with integrated antennas perform best when the access point is mounted on horizontal surfaces such as a table top or ceiling. For advanced features such as voice, location, and rogue access point detection, ceiling mounting is strongly recommended.”
First choice for best coverage: mount to ceiling. Second choice for next-best coverage: set flat on table-top or furniture top. Last choice for so-so coverage: vertical mount to wall.