[Wids]

That helps too, but it also helps to assign your characters their own personality quirks, accents, mannerisms, favored figures of speech or similar traits.

Corella almost always lies, exaggerates or says the opposite of what she means, to degrees of furtiveness or blatancy related to how much she favors, trusts and/or respects whomever she's speaking with, she demands that people address her by puffed-up titles and appellatives, she fixes Cyricists with the hairy eyeball, she's liberal with sarcasm, mockery and stealth insults when faced with someone she doesn't like and she has a penchant for fashioning and wearing disguises. Wyren and Vespera don't.

Wyren is similar to the Order of Hermes mages from Mage: The Ascension in that she speaks about magic (her favorite topic) with big words and pepperings of technical and quasi-scientific terms...this physick, that dram of phlogiston, the Fifth Seal of Praxes, a phlegmatic tincture of Aqua Fortis purified by way of a copper crucible, et cetera. She also fusses around with various small tools or vials whenever she's idle, and she's always brewing, building or calculating something if someone catches her in her shop. Corella and Vespera don't.

Vespera frequently invokes or makes oaths to Shar (in her many names and nicknames) or "the Eternal Darkness" or "the Starless Night" or similar things, she refuses to kill defenseless innocents not because she's compassionate or merciful (she's not) but because that would be honorless and beneath her (but has nothing against threatening or tormenting innocents in her usual polite yet sociopathic tone) and takes penance upon herself if she should stoop to such murders, she winces and shies away from bright light and she hums or sings funeral dirges whenever she's idling around. Corella and Wyren don't.

The differences in your characters don't have to be big enough and numerous enough to fill a chapter in a novella; just a quirk or two will do fine. Other people will usually notice (unless they're too wrapped up in their own characters or just plain oblivious to details, perhaps). Besides, you can always add more quirks or change them as campaign events come and go, so there's not so much need to get too intricate with the details.