So little things should also give away clues as to what your characters are really like deep down. I think of this as the kind of trait that a character can't completely hide/suppress. For example, a character is shown to be a "loudmouth". Fine but every so often during the story, we also spot the said character lighting a candle as a prayer for someone else. That tells me well hang on this character has another side to them. A deep, spiritual side they are either not comfortable showing more openly (they're wary of showing off their piety perhaps) or they somehow feel the need to cover that aspect of themselves up by being "loud".
So think about what little things will give away what your character is really like. These little things can also back up the main portrayal (and indeed will help make it more convincing).