May I suggest the Getting Stated Guide located at http://www.digi.com/products/xbee-rf-solutions/modules/xbee-zigbee#resources
or following the steps located at http://knowledge.digi.com/articles/Knowledge_Base_Article/Range-Testing-with-a-ZigBee-Mesh-Network/?q=zigbee+range+test&l=en_US&fs=Search&pn=1