The key to a good Wow Mage Leveling Spec is to have good damage dealing ability while also being able to attack often.
Ideally, there would be very little down time between battles.
If the down time is too much it either means the WoW Mage build is causing the player to take damage or the spells aren't doing enough damage for the amount of mana they are costing.
In order to have have a proper WoW Mage Leveling spec, a player should invest in the fire tree of spells.
These spells have the highest damage per second compared to the other mage spell trees (frost and arcane).
More damage equates to faster killing of enemies.
Faster killing of enemies means less chance to get hurt.
Less damage to the mage equals less down time healing.
I think you see where this is going.
While choosing the frost spells provides some enemy debuffs such as slowing or stopping movement, a mage fire talent build can quickly incinerate any opposition.
Besides, a dead enemy deals less damage than a slowed one any day.
The second thing to consider for a WoW Mage Leveling spec is what powers can amplify the attack spells of the mage.
Talents such as Impact and Ignite might not seem great on their own, but once combined with a powerful area of effect spell like Blast Wave or Flamestrike, they can stun or cause additional damage to multiple targets.
Same for a spell like Flame Throwing which adds range to fire spells, allowing the caster more time to cast spells as the melee targets try to close the distance.