If you want to have a good chance of passing the driving test, then you need to be confident of your driving skills ability, and that you can perform to the DSA standard on the day of your practical car driving assessment. If you don't believe that you can pass the test, then you probably won't!

          Driving Lessons

Have you taken the prerequisite number of driving lessons with an approved instructor who offers quality tuition covering the complete DSA syllabus as detailed in the driver's record. There are two things that need to be covered by anyone teaching you to drive a car before you should consider yourself confident enough to book and take the driving test.
You need to learn the driving skills as expected by the driving examiner, so for example your instructor or supervising driver will show you how to carry out the parallel parking exercise to the test standard. You also need to have enough experience of carrying out this exercise in various road conditions and situations. It is no use knowing how to do the reverse parking, manoeuvre but can't deal safely with cars or pedestrians that turn up during the manoeuvre while on the test either because you've never been in such a situation before, or you've not be told the DSA standard of dealing with such situations. Experience is very important, so get enough practise doing all the driving skills as many times as possible to boost your confidence.
 
          Believe in your instructor

If you've been preparing for the driving test with an instructor, and they advice you that you've reached the standard of the practical car assessment, then you must trust their judgment, knowledge and experience. Being nervous about it is common, but if you concentrate on the task at hand, then you should be okay.

          Driving Knowledge Builds Confidence

Another way of building confidence is if you know the rules and regulations that govern the roads that you drive on. I've lost count of the number of times a learner driver approaches a roundabout in the UK and slows down because a car seems to be driving fast towards the junction from the left. If you know that you have the right of way, then you would approach with confidence knowing that the car will have to stop for you, or have to explain why it ran into you at the roundabout.
 
If you've passed the driving theory test, then the DSA driving examiner expects you to use the information while out on the road, use the same skills you used on the hazard perception test on the road, and show the examiner what you can do.

I advice any driving test candidate to read the highway code in between lessons, to remind them of the information they gained from passing the theory test.

It is up to you be confident about your driving test, as getting that pass certificate depends on your ability to demonstrate to the DSA driving examiner, that you deserve that full British licence.