Competency questions - "tell me about a time you handled a difficult customer", "describe a situation where you led under pressure" - are not asking for your opinion on difficult customers. They are asking for one specific story with a beginning, a middle and an end, and most people answer with a vague essay instead. The STAR method exists to stop that. Situation, Task, Action, Result: four beats that turn a rambling recollection into something an interviewer can actually score against their notes.
The four parts, and where the time goes
Situation sets the scene in a sentence or two - where you were, what was happening. Task is the specific problem that landed on you. Action is what you personally did, and this is where eighty percent of your airtime belongs. Result is the outcome, with a number on it if you possibly can.
The mistake nearly everyone makes is the opposite weighting. They spend two minutes on Situation, lovingly describing the office and the team and the quarter, drift through a hazy Action, and then stop dead without ever telling you how it ended. Flip it. Keep the setup brief and spend your breath on the decisions you made and why.
Say "I", not "we"
One sentence on this because it matters more than it should: when you describe the Action, the interviewer wants to know what you did, not what your team did. "We pulled together and got it over the line" is invisible. "I rewrote the rota, took the two angriest accounts myself, and briefed the others each morning" is a person they can hire.
The common ways it falls apart
Waffling kills more answers than nerves do. If you cannot say where your story is going within fifteen seconds, the interviewer has already started worrying. Prepare six or seven flexible stories before the interview - one on leadership, one on conflict, one on a mistake you made, one on hitting a deadline - because the same well-chosen example will usually stretch to cover several different questions.
And always, always land the Result. "What happened in the end?" is the question hanging over every competency answer, and an answer with no ending feels like a joke with no punchline. Did the project ship? Did the customer stay? Did you save £40,000 or three weeks or your manager's sanity? Name it. If the result was mixed or you fell short, say what you learned and what you did differently next time - interviewers trust that far more than a suspiciously flawless win.
Practise out loud, not in your head. The story that sounds crisp in your mind has a habit of unravelling the second you hear your own voice say it.