Here are 3 links on What to Pray during Gathas / Muktad. Hope you will find them useful :

http://ilme-khshnoom.blogspot.in/2012/08/prayers-during-muktad-and-gatha-days.html

http://www.frashogard.com/what-to-do-and-pray-during-the-muktad-part-1/

http://www.frashogard.com/what-to-do-and-pray-during-the-muktad-part-2/