Most spells require the caster speak the necessary incantations in a firm, commanding voice, while making various needed gestures in an obvious manner (when you're trying to override the laws of physics through the power of your will, it generally doesn't pay to half-ass your way through it). A few spells, when noted, might only require the incantations be spoken softly, or that a few subtle gestures be made. Even rarer still are those spells that might not require any spoken or physical actions on the caster's part.
Casters of sufficient skill can attempt to get around these limitations, though it is not easy. A spellcaster casting a spell whose Rank is five levels less than their personal character level can cast a spell that normally requires a loud spoken incantation with but a whisper at a -2 penalty, and with double the normal Essence Cost. If the caster's character level is ten levels higher than the spell Rank, then a loud incantation may be performed silently with a -2 spellcasting penalty, at x2 the Essence Cost. Also, a loud incantation may be uttered softly, or an incantation spoken softly may not be spoken at all with a -1 penalty, and at x3/2 the Essence Cost.
Likewise, similar modifications of the required gestures needed for a spell (bold gestures to subtle gestures to no physical motion required) can also be attempted by casters of sufficient skill for simpler spells, with penalties and EC modifiers similar to those for modifying the spoken requirements of a spell. These modifies are cumulative: If a 6th level spellcaster is casting a 1st Rank spell which normally requires both loud incantations and sweeping gestures, to cast that spell with a softly spoken whisper and a few wiggles of their fingers would incur a -4 spellcasting penalty, and have a x4 Essence Cost.
(if an Expert is casting a spell, their character level is halved (round up) for these purposes)
Using a wand or a staff that has been properly 'attuned' to the individual caster grants a +1 on any spellcasting rolls.
Names: +1 modifier for knowing a common nickname for a target, +2 for using their true name.
Time of Birth: +1 for casting on the target's birthday, +1 for casting during the hour of their birth.
Imagery: +1 for using a rough drawing or a crude doll of the target, +2 if using a fine portrait or a detailed doll of the target.
Association: +1 if the caster has an object that is sometimes used by the target, +2 if the caster has clothing commonly worn, or an object of strong emotional meaning to the target, +3 if the caster has part of the trget's body (a lock of hair, nail clippings, blood, etc).