Well I used to be able to pull out an essay on the spot without doing a plan of somesort, but when I did that during my trials I only got 16/20 for my brecht essay and 13/20 for my incomplete Australian theatre essay (I spent too much time on Brecht...). Thinking takes too much time...
What I'm doing this time is like what grk_styl said, I wrote 2 long generic essays, one for Brecht and one for Australian. For Brecht I simply made up a focus/link between my two Brecht texts (Threepenny and Mother Courage), as I have noticed that Brecht questions always asks something about what is Brecht's intent or how Brecht made his audience confront the realities of society. Then I choose 2 or 3 Brechtian techniques that can be found in each play and focus/analyse them (for eg: Breaking down the 4th wall, the spontaneous use of song and presenting the characters on stage as real people). It is important to know Brecht's intent in creating Epic theatre as probably the Brecht essay questions revolves around this.
For Australian theatre, well I'm just going to buls**t here because the questions for this topic are just too diverse. When I wrote my generic essay, it was written in an entirely different style from my Brecht one. This time I have to look out for 6 separate techniques, 3 from each play (Gary's House and 7stages of Grieving). It is recommended that you read the introductions of each play you're doing as they often give you indications on what techniques the play used and their function or symbolism. When choosing techniques, choose the most prominant ones from each play (for eg: 7 Stages- Aboriginal Storytelling methods as well as other different styles of delivery; Gary's House- The use of stereotypes and the house as a metaphor...) as the questions would of course ask you about what techniques are used and s**t...
Well that's what I've done and I have no guarantee that it will work... but what's more important is your interest in the topic; since I'm more interested in politics and social problems then I would have more to write on Brecht than I would on Australian theatre, so therefore I would focus on that essay first and do my weaker one last. Luckily unlike the english exams, I have five extra minutes to do each essay so I might have a chance in doing well in Drama... *praying*