Padolak's advice is great. I'll give it a shot, as well, just to mix in another perspective--specifically re: necro/mage/weaver.
Skills
Magery - Your skill in magery determines your likelihood to cast magery spells successfully. Your skill level also affects the amount of hit points healed with magery spells.
Evaluating Intelligence - Your skill in eval determines the amount of damage your magery spells will do. (Note: this is true of every spell except for mind blast, which instead relies on your magery skill level and intelligence to deal damage).
Meditation - This skill causes you to regenerate mana more quickly.
Necromancy - In addition to two area of effect spells (wither and poison strike), necromancy allows the ability to summon creatures that do not require follower slots (animate dead). Moreover, the necromancy spell "evil omen" will enhance the effect of your next spell, allowing a mage with no poisoning ability to cast greater poison (as opposed to lesser poison). Most importantly, necromancy allows for the use of various forums - for example, wraith form, which allows you to leech mana based upon the amount of damage you deal.
Spirit Speak - In addition to providing you with a mana-free method for healing, spirit speak determines how much damage your necromancy spells will do.
Spellweaving - Spellweaving can be a powerful asset to any template, both in terms of damage and survivability. The Word of Death spell is the most powerful spell in the game: with a level 6 focus and spell damage increasing items, this spell can potentially deal 666 points of damage each time it is used. Spellweaving also provides more independence through greater survivability with spells such as gift of life, which allows you to self-resurrect, gift of renewal, which regenerates your health, and attunement, which absorbs a portion of the damage you take.
Templates
Standard Necro/Mage/Weaver
120 Magery
120 Meditation
120 Evaluating Intelligence
120 Necromancy
120 Spirit Speak
120 Spellweaving
Cost- or Skill-Effective Necro/Mage/Weaver
120 Meditation
120 Evaluating Intelligence
120 Spirit Speak
115 Magery
115 Spellweaving
105 Necromancy
25 [Whatever Skill You'd Like - perhaps focus for extra mana]
Stats
Dexterity - Dexterity is the least important of your stats. I like to set my dexterity to 20, but you are safe going as low as 10.
Strength - Personally, I like to have as much strength and hit point increasing items to bring me close to 120 hit points (usually around 110 strength for me). However, if you cannot afford a stat scroll, you can go lower.
Intelligence - Intelligence determines your mana pool, making it the most important stat for this template. I would recommend bringing it to 125 or higher.
Suit
Ideally, you want your suit to have 100 lower reagent cost, 40 lower mana cost, 6+ mana regeneration, 4/6 casting, 45 defense chance increase, +20 magery skill in order to use a mage weapon, and 60s resists. Unfortunately, this suit can be expensive to craft.
A more cost-effective suit should focus on the bare essentials, including 100 lrc, 40 lmc, 2/6, and 6+ mr.
Expensive Suit Example
Artifacts - Folded Steel Reading Glasses, Armor of Fortune, Inquisitor's Resolution, Crystalline Ring, Ornament of the Magician, Quiver of Infinity, Arcane Shield, Cloak of Death, Crimson Cincture, Scrapper's Compendium
Runic/Imbued Items - Gorget, arms, legs, -20 mage weapon
Less Expensive Suit Example
Artifacts - Kasa of the Ra-jin, Pendant of the Magi, Rune Beetle Carapace, Stitcher's Mittens (elves only), Chaos Museum of Vesper Shield, Scrapper's Compendium
Runic/Imbued Items - Arms, legs
Custom Jewelry - Ring and Bracelet that add to 2 faster casting and 3 faster cast recovery
Tactics
With low level spawn, use wraith form and wither.
For peerless/champs, use wraith form when possible and cast spell combinations. Here's an example of a spell combo I use:
Corpse Skin (makes your enemy more vulnerable to fire and poison damage), explosion, flamestrike, flamestrike, etc.
When the champ/peerless's hit points drop below 1/3rd of their original value, remove your mage weapon, equip your scapper's, and cast Word of Death repeatedly. Thanks to the mana you leech through wraith form, you can cast Word of Death indefinitely.
Macros
Everyone should adjust their macros according to their individual needs and playstyle. However, in case anyone needs a baseline recommendation, here's what I use:
F1 - Heal
F2 – Greater Heal
F3 - Cure
F4 - Invisibility
F5 - Fireball
F6 - Lightning
F7 - Mind Blast
F8 - Energy Bolt
F9 - Explosion
F10 - Flame Strike
F11 - Earthquake
F12 - Poison
Shift + F3 - Arch Cure
` - Spirit Speak
1 - Energy Vortex
2 - Mass Dispel
3 -
4 - Wither
5 - Poison Strike
6 - Pain Spike
7 - Strangle
8 - Corpse Skin
9 - Evil Omen
0 - Blood Oath
Mouse Wheel Up - Target Last
Mouse Wheel Down - Target Self
I also have a number of spells on my desktop:
[Edited on 12/19/2009 by Taylor V. Smith]