1). As with any piece of writing, knowing your audience is paramount. If you’re writing a summary of a play for a general audience, your “voice” should be different than if you’re writing an academic paper.
2). In the case of writing a synposis for a general audience, no spoilers, if at all possible! Try to avoid giving away any big surprises. Be especially careful about giving away the ending! Find a way to characterize these moments without detailing them. The exception, of course, is for plays where the ending is a cultural artifact with which everyone is familiar…but even then, your piece may be read by the one person who doesn’t know that Rosebud is the sled, so if you’re going to drop a bomb, drop a smart bomb. An example of walking this narrow line, from my summary of Romeo and Juliet: “Hearing she has died and not wishing to live without his Juliet, Romeo buys poison for himself and travels to her graveside. Juliet awakens from her death-like sleep, but not in time to forestall their tragic destiny.” Note: The “no spoilers” injunction doesn’t apply to a synopsis that’s part of an academic paper. Your professors are presumed to have read the play or plays…or be too jaded to care. Also, any analysis that doesn’t reflect on the end of the play is probably not a very good analysis.
3). The synposis isn’t a blow-by-blow account of the play’s action. It’s a review of the play’s main action as it relates to the dramatic through-line of the protagonist.
4). Describe characters with succinct phrases that locate them in the world of the play and in relationship to each other (sometimes, these are the same thing). Frequently, the playwright is helpful in this regard, including notes about the dramatis personae.
5). Speaking of characters, remember who the play is about: the protagonist. As fascinating as Mercutio and Tybalt may be, the play is called Romeo and Juliet for a reason. Don’t get sidetracked. If you don’t know who the play is about, don’t start the synposis until you do.
6). Tell the story clearly, only adding the details necessary to the main action or, if the synopsis is part of a larger piece of writing, that are relevant to the analysis you are performing. (Again: Don’t get sidetracked.)
7). It’s sometimes helpful to outline the main points of the plot before you start writing. This will help you see where you can take shortcuts and avoid getting bogged down in recounting action irrelevant to that all important main action.
8). You must take shortcuts. One way to do this is to look for active verbs that help you condense complex interactions that are not relevant to the main action. For example, in my synopsis of Strictly Dishonorable by Preston Sturges, I took a funny scene between three characters and summarized it thusly: “The Judge and his friend, Mulligan the beat cop, conspire to have Henry tangled up in the legal system for the evening” That’s several pages of dialogue reduced to a single sentence…but the funny scene is only there to get the two main characters alone together. The play isn’t about The Judge, Mulligan, or Henry. It’s about the main characters.
9). In shorter synopses, you can often get by without quoting from the text at all.
10). In longer synposes, especially those in service of an analysis of the play, feel free to quote where necessary. In many cases, a few short quotations will usually suffice. If you’re working toward a larger analytical point, you may single out longer passages for quotation if they are relevant to that point.