Apart from good luck, and no matter what anybody says, you will be nervous, we've all gone through it and felt exactly the same as you do, that means that airline pilots are either human, or big girls blouses, the ex would most definitely say the latter!
With the test, remember why you are doing it, and what they are looking for. Specifically, you are the acting commander, therefore make command decisions. If something unexpected crops up such as a late runway change from the one you planned for in the briefing room at 6am for a 2pm flight, what would you do? Go to the hold, clear your head, make a plan and go for it, tell the examiner what you are going to do, and if it is sensible he/she will just say ok, and watch you get on with it, then it is up to you not to mess it up with dodgy tracking.
Don't rush, only leave the hold when you are good and ready, when everything is briefed, the nav aids are set and identified, the last thing you want is to set things up going outbound on a procedure, that is when you will bust altitudes and not track, another lap of the hold could be the difference of £40 in hire costs or £1000 for a retest and training.
Show situational awareness, small things to show the examiner you have considered things such as ATIS change, usually it changes 20 past and 50 past, have a quick check of your watch and if you see its a couple of minutes to go, say to the examiner "I'm going to wait a couple of minutes to get the latest weather" but on the other hand getting the weather nice and early so to build a good picture as to what the active runway is and what approach to expect.
Make sure you follow the performance you worked out, for example, on my test the runway in use we could depart without a full back track and reduced power at that, but of course both reduction in power and reduced runway distance required factors in the performance. I had factored for the lack of runway but forgot to factor the power, therefore full power. I outright forgot, but I bullshined my way through it and said I didn't want to combine 2 factors into my performance, if I was going to have a reduced runway length I wanted full power, and he bought it until I lined up on the runway, he knew I forgot, but was looking to make sure I did exactly what I planed for, and not do a reduced power take off from a shortened runway that I hadn't got the performance data for!
These are only small things, your instructor wont put you to test if they don't think you are good enough, the only person you need to convince that you are good enough, is yourself! Showing the examiner too of course!
Hope some of the stuff is of some use. Good luck.
CJH.