Excerpt from the old forum about Sir_Toejam's Mage tips

well, the spells that i found that made the game easy were the following:

1. freeze (or course - at level 3 this is just a major pain saver)
2. burning wall - seems underpowered at 1st, but once you get it up to level 3, only enemies immune to lightning stand much of a chance against it. Works great to trap and fry large groups of critters, and combined with freeze, you can use it to make a tight box around a boss, and they will get hit by all 4 sides of the box at once (so about 100pts of damage per second).
3. leech life - usefull even at level 1 against boss monsters to get their hps down in a hurry, it is devastating at level 3 and higher.
4. hellspikes - again, starts being very powerfull starting at level 3. level 5 can take out most normal critters (including those annoying imps) in one shot most of the time.
5. divine death - while most folks frown on the divine spells, this will take out any creature in the game, excepting the black ring bosses, even at level 1 (kill a 7500 hp dragon rider with one shot!), especially when combined with my absolute favorite and most utilitarian spell:
6. Curse (survivor path) - both of the curse spells are cumulative (i.e., you can cast them multiple times on a single character, and their resists will continue to go down - just cast repeatededly on them without stopping for at least 5-7 castings), but only this curse spell will lower spirit resistance, so you can use freeze, leech, or divine death on those high hitpoint, very dangerous critters.
7. lead limbs - for very fast bosses (like the thing in the cave guarding the silver armor); it needs to be at least level 3, but is very usefull to slow powerfull mellee bosses down so you can get a few spells in before they can get to you (e.g., slow, freeze, leech, spike; repeat if necessary)

meteor strike is of course usefull in the beginning areas, but you never really need to spend more than a few points on it

don't forget to constantly check for magic books at the merchants, and try trading with everyone you meet in case they have one too. many of my skill were maxed by books instead of me spending skill points on them. I never found any books for the 8th spell type within any given class, tho, so if you like the highest level spells, that's where to spend your points.

as an example of this strategy, I killed what most people think is the toughest boss in the game (Josephina) in less than 3 seconds by doing the following:
Killing Josephina
4 quick curses (level 5), freeze (level 4), 4 leeches (level 5), one hellspike (level 5). if you can click fast enough, you should be able to beat my time.

Killing dragonriders are even easier: 4 quick curses (level 5), one divine death (level 3). takes about 2 seconds. your only danger is if they see you 1st and get a freeze spell in on you before you can cast curse on them.

general:

spend most of your ability points on agility, to keep from being hit to begin with. my rule of thumb was to keep my agility high enough so that a monster of the same level as myself would have less than a 50% chance to hit me. Once I started getting the larger dex charms, I drove that down to less than 30% chance to hit me.
Equipment Use a shield and armor and helm that have as high an armor class as possible. use a one handed weapon that drains mana (at least level 4) to restore mana when you have something frozen, so you don't have to use so many potions. whatever one-hander you decide on, you don't need to put more than 1 point into it.
don't worry about your int too much, as you can use mana charms later to boost your total mana supply; same with your con. worry about strength to make requirements for armor and a good one-handed weapon, you can stop putting in points into strength once you hit 65 (plate armor requirement).

point distribution, I would do the following:
agility 1st (unless already below 50% chance to be hit) - then
strength (up to 65) - then
int - then
con.

Sounds a bit odd for a mage, but you will still have enough mana this way, and once your strength is above 65, you can concentrate more on your int and con until you find good mana and vit charms. Remember, with low con, your best bet is to not get hit to begin with, so keep your agility high.