start with basic energy training(feeling, controlling, reading, manipulation and just its use in its raw form, also learn to read and use its spectrum) and meditation, following link should be of some help.
http://www.wiggage.com/witch/images/e3v3.pdf
After you are done with it start your study on spirits, angels, demons and other energy(spiritual) beings.
Then move on to cleansing, protection, binding and banishment spells, rituals and charms.
Do NOT STOP with energy training and meditation.
And finally you can start with attempts to contact beings on spiritual and/or astral plane just be sure to start small.
!!!BE SURE THAT SAFETY MEASURES ARE IN PLACE!!!
First can you inform us why and how much knowledge and experience plus the information you know about this? To begin, just to "begin" I would start out learning about the human body. How it ticks, how it works, if you hit this what happens, if this goes out what happens. Make sure you know all your magickal basics and then some. To be a decent necromancer you need to be skilled in many fields. Try to learn some chi healing as well, if you can use your raw energy then you can channel it better when you need to start your own necroworkings. Learn about chi in it's whole, master it, make it one of your best skills. Know about the defenses and what may latch onto souls and what a soul is, the different types of ways things exist, and continue to exist even when their body no longer does.. That'll be a good start.
Necromancy has to do with the dead. Conversing with the dead, raising the spirit (soul) of the dead, or actually raising the dead to life!
It's been around a long time, but nobody has ever proved that it works.
Most of my ancestors are buried in the same graveyard, and I have often sat amongst the graves where I can almost "feel" their presence. It is an illusion, of course! They really are dead!
Ok Brysing you are only partially correct about necromancy.
To begin with necromancy is more like a study/theoretical branch of magic, than lets use expression practical, and while yes practitioners of said form do contact spirits only those that have allowed there practice to robe them of there sanity(fairly real risk for those with any form of success in it) will try and fail miserably.
As for my my previous post being common its because it is, and not just for new age practitioners of magic but was pretty common even in antic times only difference was in form used due to cultural differences.