The interview is your opportunity to sell yourself.  The following guidelines should help.

Before
Well in advance of the interview, read through the job description and consider where your experience is relevant or otherwise.  If you lack some of the required skills, this is likely to be an area of focus during the interview. 

Be prepared to discuss how your other experience compensates, or to say how you intend to overcome any deficiencies.  Do remember, though, that a job description is written before suitable candidates are found and it's often the case that the right candidate for the job will possess some of the required experience but not all.

Anticipate and prepare answers to some of the standard interview questions that often get asked.  You know the ones. 

Prepare some questions of your own.
Visit the company's website and find out as much as you can. 

Make sure that you know how to get to the place where the interview will be held.  Take a copy of the address and contact details in case of location confusion.  Leave more time for the journey than you think you will need.

Allow plenty of time for the interview itself and remember that it might run on longer than you expect. 
Don't be late - but if you are delayed en route then call ahead, explain your situation and give a realistic revised arrival time. 

Switch off your mobile phone when you arrive.

Be nice to the receptionist - you might be working there soon!

During  
First impressions really do count.  Make sure your appearance is appropriately professional.  Don't wear 'comedy' ties or socks.

Give a handshake that is firm without crushing.   Maintain frequent eye contact but don't stare.  Smile.  Be yourself.
Answer the questions that are asked, and check that you are on the right lines if you sense that you may be going off at a tangent.

Don't smoke.  Avoid telling inappropriate or unfunny jokes.

Be aware of your body language; promote positive signals and limit negative ones.

Don't undersell yourself - talk about your positive points, without being arrogant. 

Don't criticise your current or last employer too much. 

If you don't know the answer to a question, say so.  In technical interviews, say how you would go about finding out.
Ask any relevant questions that haven't been answered already.

Don't talk about salary / rate unless the interviewer raises the subject.  Be honest and realistic about your earning expectations, and make sure that what you say is consistent with what you said when first applying for the job. 

At the end of the interview, ask what the next stage will be.  Ask the interviewer if he / she thinks that you are the sort of person they are looking to employ.

After
Call us after the interview with your feedback.  We will then talk to the client to get their impressions and contact you back to discuss the next step.