Quote Originally Posted by 'Fursphere',index.php?page=Thread&postID=145843#po st145843
Open your spellbook - cast - and watch want fires the GCD.
This^ or throw all your abilites on your castbars and start using abilites and watch and note which ones procs the same GCD's.

On a side note, if you want to try out experimental macros prior to going out in the field and using them, the best place to go would be to hit up the target dummies and try out what does and does not work instead of having to deal with mobs dying too fast to realize if your macros are working properly only to find out much later that they aren't.