You can always use the question mark ? to find out the settings you can make.
Also the help topic or help apropos are great commands;
# help topic interfaces mac
set interfaces ge-0/0/6 mac 00:2d:88:12:26:91
# set interfaces ge-0/0/6 ?
Possible completions:
accounting-profile Accounting profile name
+ apply-groups Groups from which to inherit configuration data
+ apply-groups-except Don't inherit configuration data from these groups
description Text description of interface
disable Disable this interface
encapsulation Physical link-layer encapsulation
flexible-vlan-tagging Support for no tagging, or single and double 802.1q VLAN tagging
> gigether-options Gigabit Ethernet interface-specific options
gratuitous-arp-reply Enable gratuitous ARP reply
> hold-time Hold time for link up and link down
link-mode Link operational mode
mac Hardware MAC address