I just took and passed my Instrument Ride last week. It went well, but due to the traffic south of the Phoenix area, it was a bit stressful to say the least. Realistic, but stressful none the less.
Try to find out who your examiner is going to be and what their testing style is. Though I was obviously responsible for all of the information, it isn't a bad idea to find out what approaches he/she likes to do for the ride and what areas they REALY like to talk about.
For instance, my examiner was huge on altitudes (density calculations and such). Realize that even if it is not in the PTS, you are still responsible for the info (Private Pilot Stuff can still come up). Know your systems, all of them to include brakes and various situations involved with them.
It is also helpful to talk (out loud) to yourself during the checkride and explain every thing that you are doing and things that you are looking for. This may help to answer something that the Examiner has not had the opportunity to ask and now won't because you just mentioned it. And talk about everything.
You are still pilot in command and the examiner is still going to try to do the normal distraction stuff. If you need to tell them to hold on a minute while you do something tell them so (but do it in a very polite way). That shows them that you are taking this seriously.
Here is a VOR situation that I was tested on, an fortunately my Instructor prepared me very well for this. VOR approach. At the IAF DME failure, VOR #2 failure, Vaccuum Failure. All I had was VOR #1, magnetic compass, and timer (Pitot-Statics were also ok). In the past, some students were not prepared for this one and pink slipped out.
In preparation for this. My instructor insisted that I realy KNOW my magnetic compass. We did three training flights just prior to the checkride, where the magnetic compass was all I used. It helped me huge. Especially when the DG on the aircraft I was using for the checkride went sour during the checkride. Old Murphy showed his ugly head that day. In the end all went well and my examiner just wanted to see if I knew my stuff. I did and it went well. If there was any minor errors on my part, I listened intently and was very greatful for the information and advice. Hope this helps....