Basics
A Necromancer's Place
The necromancer has a number of useful roles it can play. Equipped with armor-ignoring spells, they can be useful for direct damage. With a large assortment of hexes and debuffs, it can play a more offensive support role. Otherwise, it can create its own army composed of undead minions and use them to roll over anyone standing in their path. In addition to its offensive capabilities, a necro has skills to increase the health and energy of allies, but usually at the cost of its own health.
Being a Necromancer
Necromancers have become in fairly large demand in both PvE and PvP. The role of a necro can vary widely, playing both supportive and offensive positions. It helps knowing what roles are suited for different situations. For example, a mission with a bounty of corpses is wonderful for creating undead minions, but when fighting a large number of undead or elementals, their corpses may not be there when you need them.
Many of the useful necromancer skills require the caster to sacrifice life. It is possible to kill one's self by attempting to use one of these skills when heavily damaged and thus must watch the health bar carefully while under attack. Minion masters have even more to worry about when teamed with other minion masters, as the sacrifice from Blood of the Master affects all allied minions and raises the sacrificed life.
While in demand for both PvP and PvE, the necessary roles may be much different. In PvE, AI mobs often may clump up, making Spiteful Spirit incredibly powerful, but in PvP, smart foes will often know better than to keep mindlessly attacking.
An important aspect of battle, especially in PvP is corpse control. Only necromancers can currently exploit corpses, and if none of your team can, it can put it at a disadvantage if the other team does. If using wells or minions, the necromancer must keep a sharp eye out for when anything dies. The energy gain from Soul Reaping, experience gain, and faction gain can be used for this purpose, as it may not be easy to actually watch everything in the battle. Once fallen, a corpse can be used by friend or foe, so its best to use it before your enemies can. Minions have a fairly long cast time, and it is possible an enemy (or ally) could use the corpse for a Well Spell or another faster casting spell before the minion is created. In such a case, the energy used is wasted if there are no corpses when the spell completes.
Attribute Distribution
Most necromancers focus heavily into one of the three main attributes of Blood Magic, Curses, or Death Magic. Most will either put the remaining points into skills related to their secondary class or into the primary necromancer attribute, Soul Reaping.
Soul Reaping:
Soul Reaping is a mixed blessing. In large, heavy battles where things die frequently, it can easily supply vast amounts of energy. However, in long drawn battles with large amounts of healing keeping everyone alive, expensive hexes may easily run dry and reduce the necromancer's effectiveness. Minion masters especially focus on Soul Reaping to fund their expensive minion spells.
Blood Magic:
With an arsenal of vampiric skills and hexes, a blood necromancer can simultaneously hurt their foes while healing themselves. All life-stealing skills ignore armor, allowing them to work effectively against warriors as well as casters. A number of blood skills also aim at granting health or energy regeneration to allies, making blood quite useful. Furthermore, the enchantment Awaken the Blood increases the attribute by an extra two points, allowing a necromancer to easily achieve 18 effective attribute points for dealing draining life.
Curses:
A large number of the game's debuffs are found here. Hexes that cause health degeneration, energy degeneration, healing reduction, attack speed reduction, self-damaging effects, cause Weakness, enchantment removal, or just extra damage can all be found in this one place. Most of these skills are used to pressure an enemy and cover the team's weaknesses.
Death Magic:
Masters of the dead, these necromancers tend to focus on creating their own small army of Undead minions. While often the weakest members of the party at the start of a zone, an army of minions can build momentum and tear through many PvE zones. They also are quite effective in PvP in large battles with many corpses, but not as much in the smaller arenas. A number of direct damage spells and numerous other spells to target corpses can be found here as well.
Equipment
Armor & Runes
Many of the choices of Necromancer armor are related to the roles of the necromancer. Tormentor's Armor is fairly good as a default armor, as it raises defense and few enemies use smiting prayers in response. Otherwise, a minion master may consider armor fashioned for it, but beware that the armor will lose its strength if the minions are killed, when the MM needs it the most. Energy granting armor is popular due to the expense of many necromancer skills. As for runes, many will lend towards a superior rune in their primary attribute. The more superior and major runes one has equipped, the less health they sacrifice with skills, but it raises the risk of being killed by enemies.
Necromancers also have unique Bloodstained Boots which reduce cast time for any spell targetting a corpse. These are highly recommended for minion masters or those trying to establish corpse control.
Weapons
The typical caster selection of wands, staves, and offhand items is available to the necromancer. Keep in mind that using weapons with Hale staff heads or wrappings of Fortitude will increase health, but also health sacrificed when using sacrificial skills.
Combat Tactics
The way a necromancer fights largely varies depending on the role it is playing. Minion masters should look into the General minion mastery guide for details on the unique way they operate. Otherwise, as a caster it is usually best to keep away from enemies. If using hexes, try to keep important hexes covered by less important ones to protect against removal. Furthermore, spam hexes across different opponents if possible to apply pressure on enemy monks and to hide who your stronger hexes are on. If using wells, call them as you cast to let your team know they are friendly.