How do I tell if I'm doing well in an interview?

When it comes to doing interviews, you'll rarely be told how well you've done.
Obviously if you get the job, then you'll assume you did well, but in so many cases, when you haven't got the job, it helps to work out if there was something you could have done better, so you can improve for the next time.
Generally
Most opinions about candidates are formed within the first few minutes (that's why it's hard to overcome a bad first impression).
If an interview is less than its allotted time, it's generally not a good sign. If you exceed this time, and the interview is flowing enthusiastically and evenly between you and the interviewer, it augers well.
Many interviews are in that grey area, between outright good and bad, and so with a bit of common sense and objectivity you can begin to assess yourself – and improve. During any interview there are many signs that indicate how well you are doing – so you need to be aware of them.
Tell tale signs and clues
Naturally, you are concerned to give a good impression so watching the interviewer's reactions are a good starting point.
As you talk and give an account of your abilities, is the interviewer taking notes and following you up on your statements? If they are taking notes this is generally a good sign, as they'll be used as discussion points.
Does the interviewer probe your answers and try to find out more about you? This may appear intimidating, but it shows they are not merely going through the motions with you.
Alternatively, be aware of negative signals as well. An interviewer simply putting down their pen or not following you up on your answers means that you are failing to engage. Let's not pretend all interviewers are perfect – no matter how badly your interview is going, an interviewer who continually looks at their watch or their Blackberry is not really doing their job.
Questions or conversation
Talking about yourself is what an interview is all about, but you need to take the interviewer with you. The way to ascertain whether you are doing this is if you are being engaged in dialogue. Generally, if your interview is going well when there is a dialogue between you and the interviewer.
Instead of your interview being a list of questions and answers, it becomes more conversational. If there is a natural, even and enthusiastic exchange of information it means both sides are interested. The conversation can be regarding past achievements, aspirations or the job itself – the main thing is you're engaging, rather than simply answering.
A few quick pointers
- Encouragement?
You may be shy or inexperienced, but a good interviewer will encourage you to talk further, this in itself is a good sign, because it means all is going well. - Did you ask questions?
If you are genuinely interested in a role, you would naturally be expected to ask questions about it? Were you invited to do so? Being invited to ask questions is part of most job interviews and of the engagement process – so use it. - Were you asked about timing?
It's a good sign if you're asked about your availability. This is a factor that is of direct importance to an interviewer and wouldn't be asked of someone who wasn't ‘in the frame'. - Interviewer ‘selling'
The more the interviewer talks about what is going on in their company and how you will fit in, the better. It means they are selling it to you and potentially see you as the answer to what they want.
And finally
Obviously, the more experience you have of interviews, the more accurate your self-assessment of your performance will be. As you can see from the above, the signs are all there and if you want to be really methodical, you can put a score to all of the above and give yourself a rating after each interview, so that you can improve if necessary.