Mana will always be a problem as a mage, like everyone else said, you will always be forced to sit and drink, and quite often.
When soloing in the game, the thing you want to maximize, in my opinion, is your mana efficiency, meaning, doing most DPM(we'll see later that it increases DPS as well which is VERY important), if you don't follow me think about it like that:
At any given point you will have to kill a certain amount of mobs to gain a level, in order to do that, you'll have to cause a certain amount of damage.
The variable here, is the amount of mana needed to cause said damage, +spell damage (or spell crit for that matter) increases your damage while not increasing said spell mana cost, meaning better DPS and DPM.
Hope I got the point clear.
There should be a balance between the two of course, and this is open to debate, but my rule of thumb is to aim go for a mana pool that I can fill from scratch in 1 drink, not much more.
Usually it means going almost totally with +spell damage.
Again, this is for PvE leveling.
In instances you must also remember that mage with no mana is a mage with no damage generation, therefore mana pool should be large enough to last the entire fight while having the maximum spell damage to increase your damage output, balancing is again, a matter for personnal opinion (and very dependant on spec!)
Have a nice time leveling a mage, I found it to be quite easy so far (only 44), even after leveling a BM hunter and a feral druid, not as easy mind you, just not much harder.