I used to practise loads on my U turn after failing my first test only on that part. I used to do about 10, then scoot off and do some figure 8's, then come back and do another 10, then scoot off again down and round a few roundabouts, then back and do another 10. It also stopped me getting angry with myself if I didn't do it properly. Was also important to practise it as you do on the test, i.e. switch off and get off, walk the bike round then get back on, start and do the u turn. I sometimes found that it was harder doing that than just having been sitting on the bike all the time.