There's a difference between a two-stage interview and a second interview like the one I think you are describing.

The former - you plan to have a second interview as a part of the process.

if you see, say, eight people - there may be two who stand out heads and shoulders above the rest. it becomes very difficult to decide between them - because you are comparing them with the others - and they are both way above them. If you then have a second interview with just the two upi only compare them with each other - and it is often clear that one is far better than the other. I've used this on three or four occasions - and it has always worked for me.

My normal advice would "be yourself", but under the circumstances..... ;-)