How can I impress the examiner in the writing paper of my GCSE exam?

So the best way that I have found of impressing an examiner, is through the use of interesting phrases and tenses. Knowing some unique vocab is also good but is more of a sign of having memorised words and can also be hard to work into your passage.

For example, you can use 'si clauses' to work two tenses into one phrase:

The most common use of the Si clause is to use:

Si + Verb in Imperfect Tense + Verb in Conditional Tense

eg: Si j'étais riche, j'achèterais une voiture!

Translation: If I were rich, I would buy a car!

You could also use some idiomatic phrases that really show an understanding of french:

eg:

"tomber dans les pommes" translates literally to "To fall in the apples", but is a french idiom that actually means "to faint"

"faire l'andouille" translates literally to "To make the sausage" but actually means "to do something ridiculous"

"Avoir un poil dans la main" translates literally to "to have a hair in the hand" but means "To be lazy"

These sorts of phrases show you really know your french inside-out and are likely to impress the examiner and encourage them to give you a higher mark!