Can we use "you" to talk about people in general?
是否可以用you來(lái)代替people？

In the speaking test, it's fine to say something like "when you go on holiday, you have the chance to relax". But in a written essay, I would prefer to change this e.g. "when people go on holiday...".
在口語(yǔ)考試中，when you go on holiday, you have the chance to relax這樣的說(shuō)法沒(méi)有問(wèn)題。但在寫(xiě)作考試?yán)铮腋鼉A向改成when people go on holiday。

In the speaking test, what should I do if I understand the question but I have no idea what to say in my answer?
在口語(yǔ)考試中，如果我聽(tīng)懂了問(wèn)題但不知道說(shuō)什么的話(huà)該怎么辦？

You could use this formula: "Well, I don't really know much about... because..., but I suppose..." In other words, you admit that you don't really know what to say, you explain why, then you invent an answer anyway.你可以使用這個(gè)句型：Well, I don't really know much about... because..., but I suppose...。
換句話(huà)說(shuō)，你承認(rèn)自己不知道說(shuō)些什么，并解釋原因，然后你再虛構(gòu)一個(gè)答案。

Is it ok if my pronunciation is a mix of British and American English?
如果發(fā)音混合了英國(guó)口音和美國(guó)口音，會(huì)有問(wèn)題嗎？

Yes, that's fine. Just focus on speaking clearly.
沒(méi)問(wèn)題。重點(diǎn)在于表述清楚。

Can we use quotations in writing task 2 and the speaking test?
在長(zhǎng)作文和口語(yǔ)考試中，是否可以引用名人名言？

Personally I don't recommend including quotations because it's difficult to use them in a natural and relevant way. It usually seems like the student has 'forced' the quotation into his/her work, and this won't impress the examiner.
我個(gè)人不推薦使用名人名言。因?yàn)槟愫茈y找到和題目相關(guān)又不生硬的名言。經(jīng)常能看到考生在文章中強(qiáng)行引用名言，這并不能給考官帶來(lái)好印象。