An analysis of Glaspell's play, Trifles, should include some basic components. Aside from the introduction and conclusion (thesis is stated, and then restated), you will want to focus on the interaction of the characters, their motivations, themes that are present, and list all of the symbolism used. It doesn't hurt to do a little background study on the author so that you can see how personal influences might have played into the construction of the work. A full analysis is most likely available via the book rags site.
