Good and evil is a concept explored over and over again. I think the most common version is the question of what actually makes up evil. When is a person evil? Are evil people complex, or just bad? Does a person's actions make him or her evil? This is the issue most literature explores.
I think a good way to observe the general theme of good vs. evil is to look at the genius of Shakespeare, especially in his tragedies. There is often a lot of evil going on in the play, making people's lives miserable, ... whether it be an ambition soldier who kills in order to become king (Macbeth), or an incestuous uncle to steals his brother's crown (Hamlet), or even a pointless gang war (Romeo and Juliet).
Luckily, the definition of tragedy is such that hope reigns by the end of the play, often ending the story on a positive note. In a sense, the theme of good vs. evil often ends with good "winning," thank goodness. Recently, I have been exploring this concept in the tragedy of Macbeth by using Malcolm's final speech to his subjects as an example. The evil Macbeth has been killed and the new Scottish king, Malcolm, is set on rewarding faithful subjects and entering into a new age of justice for Scotland:
We shall not spend a large expense of time / Before we reckon with your several loves, / And make us even with you. My thanes and kinsmen. / ... As calling home our exiled friends abroad / That fled the snares of watchful tyranny, / ... By the grace of Grace / We will perform in measure, time, and place: So thanks to all at once and to each one, / Whom we invite to see us crowned at Scone.
So, there you go, yet another way that good vs. evil is presented in literature. With this being such a general question, hopefully you will get quite a set of varied responses in order to expand your knowledge of this subject of theme.
One way the theme of good versus evil may be presented is through an ironic transposition of qualities. In other words, the main character seems to represent good but turns out to do evil through naivete, ignorance, vanity, idealism untempered by truth, etc. Conversely, another character, whose behavior is called into question, actually turns out to represent good.
An example of this is Howells' short story "Editha" in which the egotistical and idealistic Editha thinks World War I represents glory and subtly manipulates her fiance into abandoning his convictions to support the war. The end reveals her appearance of good was just that: the appearance of good. Her mother says: "Well, I guess you've done a wicked thing, Editha Balcom." In a brilliant piece of foreshadowing, Editha replies: "I haven't done anything--yet."
This is fairly broad, and I am not entirely sure that you are going to get an answer you like or can work with until you give a bit more specification. Usually, in texts, the concept of "good" is embodied by a character, a specific individual, who is poised against the force of "evil," a countervailing force. For example, if you have seen the film, Schindler's List, Oskar Schindler represents the force of good and is opposed by Amon Goeth, the embodiment of evil. You would want to scour the texts or the work you are examining and look for the characters that embody qualities that would represent "good" traits of behavior. On the other side, your characters that are "evil" are going to represent those qualities that are forces of negation. In much of literature, characters are complex enough so that the distinction of "good" and "evil" are not going to be completely labeled as such and the astute reader must recognize this. Yet, in the end, authors and artists use their characters in a variety of situations to represent the concepts of "good" and "evil."