Give your characters hell. Characters aren’t meant to have a quiet life in fiction! You wouldn’t read a quiet book, would you? Do you know your characters’ individual stress levels? There’s many a tale to be told showing where characters crack and the consequences of that cracking. What secrets do your characters have? Who else knows them? Who could find them out if they suspected anything was up? Corruption exists in any world, why not your fantasy one?
Giving Your Characters a More Relaxing Time
How do your characters relax? Who do they relax with?!! Are there sports/hobbies your fantasy world encourages (and why) or disapproves of (and why)? And are there pets of any kind? If not, why not?
Characters Striking Sparks off Each Other
Characters should strike sparks off each other, else no story, but those sparks should be realistic and believable. Track records can be dropped into your story, a bit here, a bit there, which increases tension. I’ve done this with Brankaresh and Eileen. I’ve deliberately not had “one big argument scene” but hints here Eileen’s caught Brankaresh out with bad magical practice, hints there he resents her for it and so on. Don’t dump information, drip feed it. The former will slow your story up, the latter builds it. With L’Evallier I’ve hinted at his noble background, so his formal style of speech comes as no surprise. I’ve not gone into details about his posh schooling or anything like that. Think brush strokes rather than laying it all on with a trowel.