The /use_equipped_item is a very useful command because it enables you to to equip and then use an item in a macro. The “Use Item” macro step fails in this instance as it does not recognise that you’ve equipped the item. However, you can add a Command step and use the command line prompt in order to use the items immediately as they’ve been equipped, in the same macro. For an insta-cast item, this means that you can equip the item, cast it and then equip the original piece in a single macro. For non-insta-cast items, you can only do the first two steps, else the cast will be interrupted by the re-equipping. However, it is still useful to quickly equip and cast an item using macros rather than searching for the item in your inventory. See the post on Equipment Macros for more details.

Each player has 24 equipment slots, each with an assigned number. You can use these numbers in conjunction with the following commands:

/use_equipped_item #
/inventory unequip #

Posted by Taymar on http://www.mmorpg-info.org.