A concise manual on Goetic evocation. Especially notable are the author's own experiences, which any practitioner can learn from. I find his style of writing to be a little dry and not to my taste, but his skill and knowledge aren't really in question. The book is slightly intermediate, it's assumed you're familiar with the basics of a Thelema-type system of magick, so I would suggest perhaps picking up the Magician's Workbook first, by the same author. It would help you to already know the pronunciation of magickal greek and hebrew.
One of the best things about this particular goetic evocation book is that, beyond all the usual tables, sygils and names, unlike most others this book includes actual examples of evocations and what occurred. Probably the best book for starting in this work.
I give it five stars just for the in-depth descriptions of the authors own dealings with the spirits and work in the system. A treasure in its own right.