I want to have my students write a literary analysis as their assessment for this play and I need to make sure there are enough options for them to choose from.
The use of direct characterization in the play is a poignant convention in Death of a Saleman. (For example, Linda and Willie describe Biff before Biff appears on stage. Also, Willie is described by Happy, Linda, Biff and he describes himself.)
The characters both do and do not fit the direct verbal exposition with which they are presented, creating a situation of irony.
So you could lead your students to both the irony produced by these direct descriptions (Willie saying his is liked, well-liked, etc.) and you could lead your students to examine the modes of characterization in the play, especially how the direct character exposition contrasts with the deeper and more subtle characterization produced through action and relationship over the course of the play.
This play is a modern American tragedy. You could have your students think about what tragedy means to them and then have them research the traditional elements of tragedy to then analyze how Miller conforms and deviates from the expectations of the genre.
My students enjoy to conduct literary analyses, particularly the process of character analysis under the perspective of the past, the present, and the future. You may want to include in your assessment the question: What will the future hold for Biff, Happy, and Linda without Willy? It is clear that (out of the three), Biff is the only character who is round. One can argue that Happy and Linda will remain believing in the false image of Willy Loman, which is what defines them as flat characters. Yet, Biff is willing to take the plunge and open himself to new horizons.
Yet, although Linda and Happy are indeed flat characters, the depths of their characteristics are intrinsically proportional to Willy Loman's influence. Hence, conducting an analysis of the characters without the element of Willy might produce very interesting assessments of the work itself.
The contradictory nature of the dialogue of Willy is a useful element to study as a reflection of the shifting values of the culture of advertising alongside his mental demise. The erosion of faith, trust and honour is illustrated in Willy's destruction.
Flashback is a big part of Miller's style. I do think that other literary elements can feed into this. The manner in which Miller gives his character dialogue and the extended manner of speaking brings a transcendental drama to his characters. I think that this is something that can be explored. Miller allows his characters to make speeches that allow the reader/ audience to think and reflect. They are designed to deliver emotional and intellectual knockouts, one after another. For example, in Act I, Linda speaks of the disintegration of her husband with a poignancy, demanding for him to be looked at with "respect" because "he's a human being." To use this style so early in the play is something that is powerful and compelling, allowing the audience/ reader to think and to reflect about both what is being said and who is saying it. The dialogues between Ben and Willy do much of the same, in that they bring out the idea that there is a powerful level of reflection and thought integrated into extended dialogues. These help to make the flashbacks more meaningful and give more depth to the character.
I think it is safe to assume that in any literary work there are a number of literary elements that you and your students can focus on. Clearly, one of the major literary elements in this excellent play is flashbacks and their use, as you have identified, but you also might want to suggest to your students that they focus on the use of symbolism in the novel. There are a number of objects that have a symbolic importance that could be a great option for an essay on this play.
Just to give you an idea, you might want to consider the stockings that remind Willy of his sexual infidelity and cause great shame in his mind. New stockings are very important as a symbol of Willy's success and his ability to look after his family, thus it is that when Willy spies Linda mending her stockings because "they are so expensive" he feels great shame after having had a flashback when The Woman says to him "And thanks for the stockings. I love a lot of stockings." Stockings thus operate as an important symbol of Willy's infidelity and sense of shame throughout the play.