Whenever you find yourself doing one of the following things during an interview, just don’t. OK?

Don’t suck at something you say you’re an expert at

Seriously, how often do I talk to Java experts who don’t know how to use the most basic java.util classes? Or bash experts who don’t know how to grep? Or 3D math experts who don’t know anything about the dot and cross products? If you tell an interviewer you’re great at something she knows even a little bit about, she’s absolutely within her rights to test you on it. If you have no idea what she’s talking about, she’s going to start doubting everything on your resume. Don’t exaggerate your expertise.

Don’t make excuses for why you failed

Sometimes you get caught flat-footed, or your brain seizes up, or you have a bad day, or you go down the wrong path and get stuck. It happens, and a good interviewer gets that. But there’s a big difference between an interviewer who won’t support hiring you, and one who’s actively trying to veto your application. Trying to explain to the interviewer why her question isn’t valid, or why it makes sense that you weren’t prepared, or why you’re rusty in this thing you just said you do every day, is just going to make you look like someone who avoids responsibility for your mistakes.

Don’t be arrogant, don’t act superior, don’t be a dick

Should be a no-brainer, right? And yet…

Don’t badmouth an old employer

Even if you worked for Satan in the helpdesk department of the third circle of hell, it’s unprofessional to trashtalk an old employer. Repeat after me: you had a great time and learned a lot, but it was time to move on. If you didn’t stay long and/or were fired, then you left because it was a bad fit. Maybe you were looking for a different kind of challenge. Or you didn’t feel that the company had the kind of career options you were hoping for. There are lots of reasons you can discuss, but going on a rant about how your old boss was a schmuck and everyone on the team was an idiot is going to get you some sympathetic (if uncomfortable) head nods and an accelerated end to the interview. There’s no added value in talking down an old employer, and plenty of downside, so don’t do it.

Don’t swear

Some interviewers won’t care about your language during the interview, but others will – a lot. The problem is that you won’t necessarily know which is which. Dropping the f-bomb isn’t going to help you, and could easily cost you a job offer, so don’t.

Don’t chatter on and on

You don’t want to be labeled a “talker”. It’s good to build rapport, and to answer questions with a reasonable amount of detail – but going on and on ad nauseum won’t just be boring to your interviewer, it’ll eat into your time to do technical questions, and create the perception that you’re the opposite of a “doer”.

Don’t waste the interviewer’s (and your own) time

Don’t ask questions you can look up trivially. Don’t focus on irrelevant aspects of the job (gee, I hear you have catered lunches!). And for the love of Mel, please take the time to understand what the company does before the interview.

Don’t go in cold

There may be reasons why it seems convenient to schedule an interview for the day after you’re initially contacted, but it’s almost never a good idea. Even a little preparation will improve your odds of success, and no one in her right mind will penalize you for not being immediately available. Give yourself a week to brush up on your interviewing skills, research the company, and think about what you want to ask your interviewers. Having good questions is important for two reasons – first, it’ll help you determine whether the company and job are right for you; second, it’s more interesting and impressive to your interviewer.

The major exception to this is college career fairs. It’s perfectly normal for companies to set up bulk interviews for the day or two after a career fair (especially if they’ve flown out to attend). These are filtering events, and the path to a real interview, afterwards. You still shouldn’t go in cold, but as an entry level candidate meeting a single interviewer for what’s typically a reduced amount of time, the requirements are a bit more generic.

Don’t mistake the roles of your interviewers

There are generally three types of interviewers: HR, technical, and hiring managers. The HR representative is there to guide you through the process – meet you at reception, show you the coffee machine, give you a tour of the office, make sure the interviewers get to you on time, debrief you when all is done, and walk you out. Her involvement in the evaluation process will depend on the company, though she’ll almost certainly be watching for any HR-specific yellow or red flags.

Technical interviewers will make up the bulk of your interviewers. They’re there to determine if you have the technical chops for the job, and to decide whether you’re a good cultural fit. Some of them will be good interviewers, some bad. Some will have unconscious biases, others… will have stronger unconscious biases. Some will be in a good mood, others not. Some will be outgoing, others stoic. None will be able to tell you about your pay package, so don’t bother asking. It’s an unfortunate fact that your performance will likely be affected dramatically by who’s on the schedule the day you come in.

You’ll typically also meet the hiring manager at some point during the interview process. Some hiring managers will do technical interviews, some will focus on behavioral questions, and (if you’re doing well) some will focus mostly on selling you on the position. This is the person who will ultimately decide whether to fight for you – if you’re a questionable hire, she’s the one who can decide that you’re worth taking a chance on. If you’re an exceptional hire, she’s the one who’ll fight for a higher compensation package. A large part of her decision will be based upon feedback from the other interviewers, but ultimately she’s going to go by her gut.

Don’t get caught by an exploding offer

No company is going to give you an open-ended offer, valid until the end of time – but assuming your timetable is reasonable, most will be willing to hold on to an offer until you’re ready to make a decision (i.e., after you’ve finished your interviews). Some, however, will try to strong-arm you into making a choice immediately with “exploding offers” – offers with short expiration periods, and the explicit purpose of preventing you from interviewing with anyone else. These are cynical, certainly, borderline unethical, and not particularly uncommon. They’re also almost always complete fabrications – unless there’s a hard project deadline that needs to be met, and which they’re counting on you to help meet, they’ll be just as happy to hire you in a month as now. Remember that once they’ve made a hire decision, the balance of power shifts – which the exploding offer attempts to hide from you. Be polite, be firm, and don’t get caught. More on this can be found here (science!).

Don’t get discouraged

As mentioned above, the interview process is, to some degree, a stochastic process that can have little or no relationship to your actual abilities. Some interviewers and companies are better at it than others, but there isn’t a good way to know this ahead of time, and there isn’t much you could do about it, even if you did.

If you completely screw up with one interviewer, put it behind you and focus on acing the next. If you don’t get an offer, don’t take it as a statement on your personal worth. Take what you can from the experience, prepare the hell out of your next interview, and move on.

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