My top tips for the test:
Don't overwhelm yourself thinking too far ahead - focus on the road you are on and getting to the next junction safely. That's it.
Listen to the instructions and don't be afraid of asking the examiner to clarify if you are not sure or haven't heard him/her correctly.
If you go the wrong way, it's fine (except if it's the wrong way up a one way street of course!). As long as you deal with the road correctly you'll be okay. Don't panic - it'll make you do erratic things. If you realise you've gone wrong - say "I'm sorry, I took the wrong road/exit... whatever - would you like me to turn round or continue?". You are being tested on your ability to drive - not to follow directions - it's a driving test, not a taxi driver test. If you are in the wrong lane or whatever it is - go with it in terms of the Highway Code - just keep the focus on safety first. They will be more impressed that you kept calm and drove safely than if you panic and try to correct it unsafely. So if you were told to go straight on and find yourself in a left turn only lane, turn left. Say "I'm sorry - I realise I'm in the wrong lane, I shall turn left here as per the road markings and to maintain safety". That shows maturity and road sense.
Part of the test includes using sat nav these days - practice that so you are used to it and comfortable with it.
If you start a manoeuvre and realise you're going wrong or your starting angle was off, don't keep going knowing it's wrong. Stop. Start again. It's fine to do that - and the examiner will prob be more impressed that you've recognised it and are correcting it safely and sensibly. As long as you keep alert to what is going on around you and manage the situation safely, it's fine. You CAN say to the examiner "I'm sorry, I wasn't quite right on the angle, I'm going to pull forward and start it again" - as long as you don't hit anything, cause a dangerous obstruction, mount the kerb or ignore what is going on around you, then it's fine. You don't want to have to do it repeatedly but they know you're likely to be nervous and a "false start" isn't the end of the world - it's how you manage it that is key.
Do what helps you focus and concentrate. If you have to repeat the examiner's instructions to yourself - verbally or in your head - do it. I always had a bit of a running commentary going on in my head - as though I was my own instructor.
Don't be afraid to talk to the examiner - you have to focus and concentrate of course, and if you need silence then that's what you have, but sometimes a little small talk can help to relax and break the ice. I had an examiner who was miserable as you like and was known for failing people. He tried his best to catch me out on things but it wasn't happening - I drove well and, if I do say so myself, my parallel park was epic! About half way through the test, he started to chat to me - not sure if he was trying to put me off - but he didn't. I relaxed more and it turned out his daughter was trying to get into the same career as I'm in. He suddenly seemed to have more respect for me and by the end of it, while he was still miserable (and didn't even congratulate me!) - his manner had changed a bit, he did pass me and it did help - but that's just me.
In my experience, a massive part of the test is how you manage situations - do you panic or do you think it through? If you stall - do you freak out or do you deal with it calmly and efficiently? Are you aware of your own driving... and of your surroundings? If you go wrong - how do you handle it? Do you calmly recognise it and deal with it, or do you panic and make the situation worse?
Above all - breathe - take your time. Focus on driving safely - that's ultimately what they want - is to see you are in control of the vehicle and can drive safely. Good luck!