When it comes to revealing your character’s reactions and attitudes, think long-term. Nancy Kress uses the term "accretion of scenes." Think of each new scene involving your character as a new "close up," showing us another aspect of the character’s inner life. In this way, you’ll add to the richness of the reading experience and not do characters "by the numbers."
One tip from master writers is to allow your characters a wide swathe of possible actions or attitudes, even if you’ve done extensive background work and think the character is locked up. When something surprising does occur (writers often say "my character just took over"), let it happen and only THEN find a way to justify it. In this way, you’ll avoid the predictable, and that will please your readers.