A few thoughts from DVSA about Practical Driving Tests

Keeping to the routine of:

• Mirrors [interior + L or R but take good note of What, Where, How Fast] 
• Signal [as appropriate rem: be UP - Right so you won't be Left - DOWN walking or riding the bus]
• Manoeuvre [DO what you need to DO - DON'T second-guess yourself!]

will keep you focussed and less likely to 'panic!'
https://www.gov.uk/government/news/dvsa-reveals-top-driving-test-faults-made-in-the-first-year-of-the-new-test