The oral exam is where most Goethe and telc candidates feel least in control, and the reason is usually that they've prepared their German without preparing the exam. These are highly structured tasks, and knowing the structure is worth more than another fifty words of vocabulary.
What these exams are
Goethe-Zertifikat and telc certificates are mapped to the CEFR levels — A1 through C2 — with B1 meaning you can handle familiar situations independently and B2 meaning you can discuss abstract topics with some fluency.
At several levels the Goethe exams are modular: reading, listening, writing and speaking can be taken and passed separately, so a failed speaking module doesn't require retaking everything. Confirm the current module rules for the level you're sitting, as they differ by exam and have changed over time.
The structure is the thing
Oral exams at these levels typically involve a short introduction, a presentation or description task, and a discussion or planning task with the examiner or another candidate.
Each part has an expected shape. A candidate who knows there's a planning task where you have to agree something with a partner behaves very differently from one encountering it cold.
Get the official model papers for your exact exam and level. They exist, they're free, and candidates who've worked through them perform visibly better.
Where marks are lost
Saying too little. The most common. Examiners can't credit what you don't say, and a short correct answer scores below a longer one with minor errors.
Not interacting in the paired task. If the task is to plan something together, the marks are partly for engaging with what the other person said. Delivering your own prepared position and stopping misses that entirely.
Treating it as a test of accuracy. Candidates who self-correct constantly, restart sentences and pause to get an ending right sound less fluent than they are. Keep going; a wrong ending costs less than a stall.
Memorised monologues. Audible, and they fit the actual prompt badly.
What to practise
Opinions with reasons. At B1 and B2, almost every task asks what you think and why. Ich finde … weil · Meiner Meinung nach · Einerseits … andererseits · Das kommt darauf an. Learn these until they're automatic.
Agreeing and disagreeing politely. The paired task needs them, and they're a register most learners haven't practised.
Describing something for a minute. Unglamorous and directly tested.
Buying time. Lassen Sie mich überlegen · Wie soll ich sagen. Better than silence, and entirely normal.
On the day
Speak slightly more slowly than feels natural. Ask for repetition if you need it — it's permitted and it costs nothing compared to answering the wrong question. And if you make an error and notice it, move on rather than returning to it.
What actually gets people through
Having spoken German out loud, regularly, with someone who makes you respond in real time. Reading, grammar work and listening all help the other modules. The speaking module is only built by speaking.