It is not uncommon to read in mundane writings concerning spell casting that each spell has its own associated way in which the wand is to be waved. However, wand waving is not a necessary part of casting a spell. After all, a talisman is essentially a small wearable wand and nobody waves a talisman around as if swatting at a fly.
However, the myth of wand waving - like most myths - does have a grain of truth to it. A mage's wand acts as an extension of her hand, and pointing it at the subject of the spell is much like pointing with the index finger. Aiming the wand at the subject of the spell helps to focus the spell and thereby increases the amount of the spell that reaches its target. And the effect of the spell is directly proportional to the amount of Quintessence that strikes the subject.