Most spells require several different components to work effectively. 

• The caster must properly speak the incantation (unless sufficiently advanced enough depending upon the spell).
• The caster must perform the required wand movements.
• The caster must, if the spell requires it, properly focus and direct the spell's initial flow of magic.
• The caster must, if the spell requires it, concentrate on the correct thoughts, feelings and desires after the spell is cast.
• The caster must, if the spell requires it, have enough magical willpower.

Let us approach each of these requirements one at a time.

Almost all spells contain some form of incantation, a series of syllables spoken in a precise manner and in exactly the right order. This is crucial; an improperly spoken spell will do nothing, if you are lucky. The spell may also have an effect never intended by the spellcaster. As Charms Master and Professor Filius Flitwick is known to say, "Never forget Wizard Baruffio, who said 's' instead of 'f' and found himself on the floor with a buffalo on his chest."

Some form of wand movement is also necessary for almost every spell. It is believed that this helps to shape the spell, along with the incantation, toward achieving the desired effect. Witches and Wizards of exceptional renown can cast spells without their wand, but such practiced spellcasters are few and far between. It takes monumentally more effort of will, focus, and concentration to perform a spell without a wand.

Some spells require that the user spend some measure of their focus on a target. One of the most elementary of spells, the Levitation Charm, requires that the caster choose a target for the spell. When a target is not properly chosen, as was the case with the Levitation Charm's inventor Jarleth Hobart, embarrassment is the least of your worries. Hobart's mistake resulted in the breaking of sixteen of his bones as well as the ridicule of his town, at least for a time. In some cases, focus may also be a particular thought, feeling, desire, or visualization. This can be instead of or in addition to focusing on the target, but the key is that the focus occurs before the spell is cast. For example, a charm typically used to disrupt a specific creature's shapeshifting requires imagining the creature's current form as somehow ridiculous before casting the spell, while also focusing on the creature itself. Both visualization and focus on the target serve to direct the spell’s initial flow of magic.

Some spells require that the user concentrate on a specific thought, feeling or desire in his or her mind after casting a spell to direct its effects. One of the most well-known examples is the Patronus Charm. This Charm requires that the user recall a very happy, very powerful memory (the focus for the spell, as described in the paragraph above) and keep it in their mind even as a Dementor attempts to feed upon it (the concentration). Only by maintaining the happy memory in his or her mind can the spellcaster prevent the spell from dissipating. See Ch. 3 if you are unfamiliar with dementors.

Finally, some spells simply require a sufficient amount of willpower to cast them. This power may come in the form of direct magical strength, though often it requires knowledge of obscure magic or concepts that are difficult for a Witch or Wizard to cast. A particular Dark Arts spell known only as Fiendfyre is obscure enough that only a few know the incantation. Of those that know, only a handful could successfully cast the spell without incinerating themselves by it. Such a spell requires an incredibly strong will and concentration to control at all.