I don't know if this advice would apply for you, but it has become pretty effective for me. But, I would say the best way to impress people is just to relax and not put too much pressure on yourself. Right before you go in the room, just say to yourself, "Who cares if I don't get this job? What is the worst thing that can happen?"
The best interviews I have done have been when I have been able to relax to the point that it turns into a very casual conversation with the interviewer(s). Whenever possible, try to be enthusiastic and interested.
Not trying to be preachy but I have also discovered some good general rules for technical interviews and how to turn them to your advantage and put them on a level where you are able to relax while discussing it. In my experience, a candidate that is willing to learn and expresses enthusiasm for learning is sometimes preferrable to the code-genius who answers every question perfectly but may exhibit a "know-it-all" attitude.
1. If asked a question about something you have never heard of, don't freese up, just say you are not familiar with it and then ask them what it is. If possible, take their answer and apply it to something you DO have experience in and relate what that experience is. You may be able to convince them that you could pick up this unknown knowledge easily. The classic example here would be a question about a particular design pattern. After finding out their answer, you can let them know what design patterns you ARE familiar with and how much you want to expand your knowledge in this area.
2. If asked a question about something that you do not have experience in, but are familiar with, say so. Then, as with #1 above, describe a similar concept that you ARE familiar with, to the extent that they are assured that you can learn that concept quickly.
3. If asked a question that you are VERY comfortable with, run with it. Try to turn the conversation about this topic into a theoretical discussion where you can ask them questions about how they view the concept, how you have seen it used and even ways that you think it could possibly be utilized but have not been able to. Make it apparent that you have knowledge and are willing to take it to the next level.
And if all that fails... picture them in YOUR underwear. :)