Path I recommend for budding spellcasters.
Generalist Mage
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Soooo... you want to learn how to terrorise people with a Mage eh? Note that different Mages have different approaches to combat. Some are party friendly and specialise with disabling magic( Hold Monster, Chaos, Feeblemind, Domination, etc... ...), some heck care their party and let loose mass spells of destruction( Fireball, Skulltrap, Meteor, Death Cloud, etc... ...), others are insane and crave total destruction( Disintergrate, Flesh to Stone, Cone of Cold, etc... ...), and many many other types, hybrids and such.
The thing is, until
you know what kind of spellcaster you want to be, you will not know which spells you will use the most. Therefore, you start off as a Generalist Mage, you will be able to cast any spells you like, you can experiment any form of combos you like.
Once you start to settle on a certain set of spells that you use all the time... we move on toooo... ...
Specialist Mage
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Go through your list, which spell school do you use the least, or not use at all? When you find out, choose a Specialist Mage with that school as its' opposition school. You now get more spell slots, you now start to really get comfortable with a Mage.
Eventually, maybe... you will start to feel limited... that somehow you wish you could be... more powerful, you may now be ready to graduate to being a... ...
Sorcerer
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You
know what spells you are going to use, you are willing to sacrifice Xp( from scribing scrolls) for more power, you want to be a total bad-ass, god-kicking, monster-munching, chest-beating, ahhhh... *cough* *cough* sorry, got carried away,

but you catch my drift.
General rule for new Sorcerer wannabes, make a spell list before you start the game. Once chosen, there is
no turning back.
Choose well, and you will what I described and more, choose foolishly or unwisely, and you will be reduced to being a medicore Mage.
Soooo... you have reached the pinnacle of spellcaster, is there anything else to do? Well... there is always the... ...
Wild Mage
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This kit is the best kit for a laugh.