NECROMANCERS HEED THIS WARNING:

Necromancy is not as simple as burning herbs, putting intention into your work, wishful thinking and candle lighting. 
That is to say: spells of necromancy can not be “made up”. 
There is a science to it, you must take into consideration the fact you are getting a spirit through the gates (or the veil) and bringing it to you, you must consider energy, you must consider location and magnetism and all variables. 
If you seek spells there are three places you should look.

Books: you may find rituals and spells in religious tomes and textbooks as well as documents concerning the tribal practices conducted by different cultures throughout time. If your only point of reference is whatever you found by googling “necromancy” then you are by no means educated in the practice.

Teachers: You can find many talented necromancers who are more than willing to teach the art (at a price). I personally aim to teach everyone who wishes to learn and provide the basics on the practice.

Spirits: Regardless of their ability in life, most spirits are capable of teaching small bits of knowledge, if it is worth their time. Do not expect a book of knowledge from them and do not expect all knowledge to be of use.

NECROMANCERS HEED THIS WARNING: NECROMANCY IS NOT A TOY,
TO ATTEMPT TO FABRICATE A RITUAL WITHOUT EXPERIENCE WILL CERTAINLY END IN FAILURE. YOU HAVE BEEN WARNED.