Well as a preparation you should take the time to dig in pprune!!
It´s all there - especially in the "middle east" forum. - Dig and read about working and living in DXB/EK.
Good info is also:
http://www.pprune.org/go.php?go=/pub.../Emirates.html
The pay is according to the website, but they´ll give you the definition of "credit hours" at the interview. (dead-heading/proceeding is the same as flying e.g. - it´s pretty decent)
Study the website and their route structure.
Show that you´ve informed yourself about the company and living in DXB. - And do it before you go for the interview!!
Why do you want to go?
What can you contribute to EK and why?
Recall all your CRM stuff!
etc.
Be yourself and enjoy the three days.
The guys are tough, but pros and decent and fair.
They want to see if you can fit in and be a captain.
Good luck.