Necromancy is very dangerous. Look for some older books, like Claviulae Salomonis and so on. Old magicians would rather evoked infernal demons than the ghosts of the dead.
On my view on anymagick practices, one thinks something is dangerous then the results will be just that form of theconstruct you've created. The death current can be frightful for most and pleasing to others. Always a good plan to have a spiritual guide either angelic or a daemon to help you through Necromancy.
The only reputable book that I can think off is called "Greek and Roman Necromancy" by Daniel Ogden. I actually managed to find this one as a free e-book, but for the life of me cannot remember from where. It is worth trying to find it. I have not read it yet. I checked on Amazon and it has got good reviews.
Its author is an actual Professor of Classics and Ancient History and is teaching in the University of Exeter.
From what I have read and heard some of the practices involved into it are pretty much illegal in most countries. Such as requiring/storing human skulls, bones and other remains, grave/tomb sitting during night, digging out graves to collect the soil near the actual body and so on and not to mention the animal sacrifice.
Also the idea behind all of these strange practices is to be able commune with the dead for the very specific idea to divine about the future. However, I have worked with the dead for 25 years, and I have met only one that actually predicted the future. Therefore, I believe that is safe to assume that most of the dead do not know the future and do not have direct access to vast knowledge just because they died. Except, for the souls that already had the gift of premonition or had access to the future for whatever reason for brief period of time. Also keep in mind the dead that are residing on the most accessible level to living humans in general are troubled souls. They are impossibly hard to work with, they experience great difficulties to focus on a particular task or sometimes they become extremely obsessed over certain event, place or energy or person. The dead who have moved to higher levels are very hard to connect with, if they do not want to be found. It is much easier to work with them, but they are very difficult to get hold on. One actually requires serious skills to pull this off and vast knowledge and experience. The dead are troublesome, defiant, pranksters and they will not cooperate just because ordered to do so. They will only break a sweat and go out of their ways for somebody they truly respect. Additionally, even if you try to control them using conjuring methods they cannot suddenly develop a skill they already did not have just because you ordered them to do so. Finding a dead soul that had the gift of premonition, when alive will be challenging. There are not that many around.
