(This is close to my heart because I’ve done a bunch of interviews lately, some good, some not so good.)
If a skill or qualification is on your resume, I will ask you about it, especially if it’s one I also have. Claim to know C# and I’ll ask you C# questions. Claim to know Java and I have a set of Java questions ready to roll. If you say you’re an ISTQB certified tester but don’t know their core testing principles from the syllabus, that’s a problem.
Never lie to me. If you didn’t do your pre-interview essay questions yourself, it will be obvious when I talk to you. I’d rather you said "I don’t know how to do that, but here’s how I might try." Even if you’re on the wrong track, a valiant attempt is far better than a copied answer.
Never ever give me someone else’s answers. Seriously. I can’t believe I have to say this. Things you found on the internet, copied in wholesale, and tried to pass off as your own leave a bad taste in my mouth.
Have some questions to ask me. Because your questions to me are also part of how I assess you. If you ask about the vacation policy, required working hours, and working from home in the interview, those questions worry me.
Don’t have sections copied and pasted from elsewhere on your resume. Why bother telling me the same stuff twice or four times? Don’t waste space and don’t waste my time.
It’s a conversation, not an interrogation. Brainstorm with me, think out loud, if I draw on the whiteboard and hand you a marker, use it. Bad art skills are never a disqualifier for software quality jobs.
Have examples to common questions ready, because I’ll ask you for specifics.
Smile. Even if you’re nervous, fake it if you have to.
Don’t bad-mouth your past or current employers. Even if they’re horrible, find a way to say it that doesn’t involve saying awful things about them. We already know there’s some reason you want to work elsewhere.
You’re interviewing us too, and this job may not be a good fit for you. Better to find that out now than take the job and hate it.
Have a reason for why this job at this company. If you don’t want to be here, I find it odd that you’d go to the trouble of interviewing.
If it’s a phone interview, make sure you answer the phone when I call. If the line is engaged or I end up in voicemail, that doesn’t start the interview off well.
Getting both in to and out of the building are also important. I had one candidate call HR to say the building was locked and she couldn’t get in. It wasn’t locked. Same candidate also walked straight past the elevators and into the kitchen when I said goodbye, and just stood there looking confused for a bit. If you can’t figure out building navigation when you’re nervous, not a good sign.