My advice: Don't treat it as a special drive, just drive as you normally do with the instructor.
- For example, don't be "extra cautious" pulling out of junctions. If you judge it to be safe to go, then go. If you miss what the examiner judges to be a reasonable gap, you'll get marked for undue hesitancy. If you drive overly cautiously and make the same hesitation mistake 3 times, the examiner may judge it a habitual error and fail you. To back this up... I was complimented on the practical driving test I took in the instructor qualifying process on my judgement of gaps, and how I wasn't afraid to pull out and put my foot down. The examiner won't be looking for the same level of judgement in an "L" test though, but the sentiment is the same - don't sit there aimlessly waiting for an enormous gap.
- Make sure you do your FULL and proper observations at junctions. A good look to the Right-Left-Right is the minimum. When you're turning left, make sure to actually be looking back to the left when you move off - don't move forward whilst your head is still turned to the right checking for traffic. By all means have another glance to the right once you've started moving and have covered a few yards. Looking where you're going as you move off is the important bit. Observation at junctions is the #1 reason people fail their tests in the UK.
- Don't get too hung up on making extravagant head movements to show you're checking your mirrors. Even the smallest "normal" mirror check movements are dead obvious when you're watching someone drive. More to the point, the examiner is actually looking for you to react to what you see in the mirrors. If someone is tailgating you, make a point of dropping back from the car in front to give yourself more room.
- Do be sure to use your mirrors when changing direction. When moving past parked cars on your side of the road, check the right mirror before moving across to go past the cars (no need to signal unless anyone will benefit). When you've passed the parked cars, check the left mirror for cyclists etc before moving back over to your side. Use of mirrors for changing direction and before speeding up/slowing down is also high on the list of top 10 test failures.