Would exercises work, though? For me a character emerges as I write him/her during the course of a story, so the verbal and physical tics arrive without conscious input from me (ie I don't think "I know, I'll have her bite her lip at this point" -- it just gets typed and I think about it afterwards) and then those tics are either consolidated or eliminated as I continue, depending on how I feel they work with the character's personality, backstory and current problems/adventures. It's a long-term relationship I'm building with the character, so I know that for me exercises wouldn't work as I wouldn't be able to invest sufficient interest in an made-for-exercise character to be able to do that.
My advice is just to write the characters and fully inhabit each of them, and let them form their own mannerisms, perhaps filched from your own tics or those of people you know. If that's not working for you within the structure of the novel, go outside it and think more about their backstory, and write scenes that simply can't be in the novel, eg a character's first day at school, or first kiss, or deathbed, and see what happens. Perhaps alongside that make a schedule of those mannerisms or speech tics, so they're all together, and just analyse if they feel right.
But if that doesn't appeal, or still isn't working for you, trying writing a short scene -- eg 600-800 words or so -- and put it up in Critiques and ask for feedback on the character alone, that is ask critiquers to say how they read the character's personality. If there's a mis-match between what they say and what you intended, ask for feedback on how best to produce what you wanted. (I'd suggest Critiques as more members visit and comment there than in Workshop, plus it gives you more than just a couple of paragraphs to play with to get the character across.)
Meanwhile, is there anything specific which you're finding difficult?