If you want to pass the driving test, you can not afford to be thinking about anything else apart from the present task at hand.
Many test candidates are so pre-occupied with the fact that they badly want to pass the dsa practical car assessment, that they don't concentrate fully on their driving. Subconciously their either trying to figure out where they are being taken on the test route, what driving maneuver they will be asked to do next or remembering what they failed their last test on, and that this is their 3rd driving attempt!
The best way to guarantee you will pass is to treat the driving test as your first attempt, concentrate fully on showing the dsa examiner that you have acquired the required skills at the set standard, and that you are ready to be allowed to gain more experience as an unsupervised safe driver.
If you make a driving mistake, don't start to think did I get a major or minor fault for that, let it go, ignore it, and still continue to give the assessment your best efforts. You need to wait until it is over before you relax. If you've had enough practise, done your homework and research well, then the 40minutes will fly by quickly. But until you've got back into the driving test centre and the examiner has told you that it's the end of the test, don't let your guard down. I've lost count of the number of stories I've heard of people failing thier dsa practical car assessment either within site of or inside the test centre car park.
One split second is all it takes, so you can't afford to think about anything on your driving test apart from the developing situation in front of you. One step at a time is all it takes, deal with the present sucessfully, and move on to the next.