For Tom Robinson, after talking about how he is presented as a good, honest man you could say how this makes the verdict of the trial shocking, and you can include context, reference the "usual disease" and how their prejudices makes them blind to the evidence that reveals Tom as innocent.
I also have some points about reader effects/personal responses you can include, linking them to themes/writers techniqes particularly empathy...
For some "good" characters you can mention how they are not perfect. For example, Scout fights, Jem destroys Mrs Dubose's flowers, Tom has been jailed before. This helps the reader to empathise with them and makes them more realistic. Empathy is also a theme of the book. This is a good thing to mention because it is to do with Lee's techniques and the effect on the reader.
Also, Bob Ewell has no redeeming features for this very purpose, the reader does not empathise with him at all and again, makes the verdict of the trial shocking as he is such a dishonest, lazy man "fired from the WPA" (this was very rare at the time).
Another thing you can say about empathy- Lee uses the children's descriptions of Boo to make the reader think he is a "malevolent phantom" or monster, but through the children growing up and gaining and moral education, she reveals that Boo is in fact simply a mockingbird or scapegoat and is a friendly man. This teaches the reader not to take things at face value and question their own prejudices.
Overall the point Lee is trying to make about empathy is that ignorance and lack of empathy is the root of prejudice. Some characters lack empathy for different reasons e.g. youth, existing prejudices, what they have learnt (Francis uses the "n word", because Aunt Alexandra is racist).
However the characters that learn to empathise (obviously scout and jem, even Aunt Alexandra is horrified when Tom is killed) give the reader hope that things can change.