There are 30 Aethyrs in Enochian magick. There is a different call to summon the angels from each aethyr. We are not experienced with this form of magick. I have merely been reading a book about this magick for more than a year.
The author of this book recommends starting at the 30th aethyr and moving down to the first aethyr. The first aethyr is supposed to be the one which is closest to God.
Here is a very popular book on Enochian Magick:
Enochian Vision Magick: An Introduction and Practical Guide to the Magick of Dr. John Dee and Edward Kelley