Most interview advice covers the basics, arrive on time, dress appropriately, research the company. Smart candidates already know that stuff. The mistakes that actually cost people jobs are subtler, and they're often made by people who thought they were prepared.
1. Treating preparation as optional because you know your subject
This is the most common mistake among experienced professionals. The logic goes: I've been doing this for years, I know my field, I'll be fine. The problem is that interviews test interview skills as much as they test job skills. Knowing your subject well doesn't mean you can communicate it under pressure without preparation.
The fix: prepare specific examples. Know which stories you'll tell, which numbers you'll cite. The content is the same, the preparation is about delivery and selection, not learning new material.
2. Over-explaining every answer
Smart people sometimes try to demonstrate their depth by giving exhaustive answers. It backfires. A two-minute answer that covers one point clearly is more impressive than a six-minute answer that covers four points vaguely. Interviewers lose the thread. They stop listening. They start wondering if you know how to be concise in meetings.
Practice giving complete answers in under two minutes. If the interviewer wants more depth, they'll ask. Let them drive.
3. Not asking questions at the end
"No, I think I have everything I need" is one of the worst ways to end an interview. It signals low engagement and missed opportunity. The questions you ask tell the interviewer how you think, show them you're thinking about the role seriously.
Have three questions prepared. If two get answered during the interview, you still have one. See our guide on questions to ask at the end of an interview for specific suggestions.
4. Badmouthing a previous employer
Even when it's completely justified, criticising a previous employer damages you more than them. The interviewer doesn't know the context. What they hear is: this person speaks poorly about past employers. When things go wrong here, they'll speak poorly about us too.
The fix: if you left because of a bad situation, be honest about wanting something different without detailing what was wrong. "I was looking for a role with more ownership over technical decisions" is fine. "My last manager micromanaged every line of code" is not.
5. Underselling achievements out of modesty
This is particularly common among people from cultures where self-promotion feels uncomfortable. In an interview, the expectation is that you will speak clearly and specifically about what you've accomplished. Saying "we did a project that went pretty well" when you should be saying "I led a team that shipped a feature used by 200,000 people and reduced churn by 15%" is a real cost.
Before your interview, list three achievements and find a number for each one. Revenue impact, time saved, users affected, error rate reduced. Numbers make achievements real.
6. Ignoring the video setup in remote interviews
Blurry camera, bad lighting, background noise, and a poor internet connection are all within your control. Every one of them creates friction that makes the interviewer's job harder. More friction means a worse impression, regardless of what you're saying.
The bar is: face well-lit, background neutral, audio clear, camera at eye level. None of this requires expensive equipment. Good natural light in front of you and headphones with a microphone solve most problems.
7. Not recovering well from a blank
Most candidates blank at some point in an interview. The ones who recover poorly let the blank become the memory. They get flustered, apologise excessively, or give a rushed, thin answer to make up for the pause.
The better approach: take 2-3 seconds, say "let me think about that for a moment," collect yourself, and give a considered answer. A brief pause followed by a good answer is remembered as a good answer. A rushed bad answer is remembered as a bad answer.
8. Skipping the follow-up
A brief email within 24 hours thanking the interviewer and referencing one specific thing from the conversation sets you apart. Most candidates don't send one. It takes three minutes and it keeps you in the interviewer's mind at exactly the moment they're comparing candidates.
Don't make it generic. "Thank you for your time, it was great to learn more about the role" goes in the bin. "Thank you for the conversation, the point you made about the direction of the platform product was something I've been thinking about since. I'm genuinely excited about this role" is a different thing entirely.