Smacky's Guide To Magic, Section 1-1: Wizardry spells

Training wizardry spells

Experience gained via casting spells goes to the wizardry spells skill, and as your level in this skill increases you will be able to cast more and more powerful spells.

You will only get experience for killing a mob with a spell. Therefore, non-offensive spells will not train wizardry spells.

Spell power and cost

The precise number of individual spells you can cast is determined by your current reserves of mana. Mana is affected by your level in wizardry spells and power.

So your mana increases as you level wizardry spells. However, the cost in mana of spells also increases (as does their effectiveness, eg, damage done) as you increase your level in this skill. Therefore there is a theoretical trade-off in levelling wizardry spells.

Some effort has been spent balancing the game so in fact the trade-off is not something with which to be overly concerned -- the practical issue to keep in mind is that as your maximum mana increases it will take longer and longer to regenerate.