"Why can't I manage to Evoke and communicate/work with External Entities successfully?"
In order to answer this question, we will have to start at the paradigm that leads up to Evocation/High Magick:
Sympathetic Magic A.K.A "Low Magick". You need to understand that before you can even attempt High Magick. You need to master the very basics first, then work your way up to a Zenith. A good place to start is Witchcraft and Chaos Magick as both of these two paradigms have a decent understanding of Sympathetic Magick and much, much more.
Think about it. Dee, Crowley, Barrett and many others did not just simply stroll into a"Temple of High Magick" and mastered it overnight! It took years of study, dedication as well as immolating ignorance in order to become Adept in this paradigm. High Magick is not simply known as HIGH MAGICK for some trivial reason. In order to even attempt Grand Necromancy, the Mage will have to be an Adept High Mage! These two Practices are closely linked to one another, unlike any other paradigm.
We see MANY Daemonolaters "attempting" to work with Daemons, however some of these individuals do not even know the basics of Magick nor fully understand it! There are many Practitioners of the Occult that follow this ignorant trend.
If you do not work yourself up from the basics, you simply won't have the Spiritual Authority, Strength and Will to successfully communicate with these Intelligences, never mind WORKING with Them! These Beings will simply use and mislead you, if you're fortunate, and you will become a slave to Them due to your inability to spiritually perceive and know beforehand when you are in fact being deceived!
Remember, these Intelligences ARE NOT your friends or Family, unless one or more becomes a Patron/Matron on your spiritual path, but this is a matter altogether different. Don't fool yourself, the minute you think you are in control, that's the moment when you have become a slave. Why? Because They exploit weakness to Their full advantage, after all - it's a simple Universal Law that the strong will dominate the weak, it's nothing personal dear reader.
High Magick is not some metaphorical rest room that you can simply walk into and relieve yourself. It takes A LOT of hard work, self discipline and dedication to master! We find it extremely ridiculous that any Tom, Dick and Harry thinks that they can simply wear High Magick as if it's some ratty robe!
Remember, there is a great difference between dabbling and practicing ACTUAL Magick. We've heard the term "mental masturbation" mentioned once or twice and this would be a good example thereof.
The result for not having developed your spiritual faculties in extent and degree and attempting High Magick will be:
1. Delusions (Mental Masturbation) - this simply means that you will unknowingly contact your subconscious, which will manifest as an Archetype and assume the role of the Intelligence you attempt to communicate with. As seen with attempted Divinations allegedly "working" through Deities and so forth. This form of actual Divination does exist (Divining via Divinities) however the spiritually inadequite will not know the difference, nor succeed.
2. You will unknowingly Evoke a Demented or Malicious Spirit and it will:
A. Mislead you
B. Destroy you
C. Possess you.
D. Manipulate you
E. All of the above and worse.
The simple truth is that the practice of High Magick requires a Great Degree of Intelligence, Creativity, Willpower, Dedication and Numen. There are many skeptical practitioners in the field of Magick (irony) that will simply scoff at these written words and shrug at best, however, we gain nothing from writing the Truth. You see dear reader, the Truth is simply perception from a uncorrupted mind, and we all have virtues and vices, however even the blind can see what is obvious and make a lucid and sane conclusion.
So kindly, do NOT dabble with the Occult, rather master the basics first and work yourself up to the path you feel suits you best. Save yourself a world of grief and find a Master Teacher of the High Arte. These teachers are spread far and wide however we are here. We are willing to teach and instruct those who are willing and capable.
Thank you for reading, we hope this post will serve you well.