A student, Kishanth, asked me about two of the points in the grammar criterion for band 8 writing (both task 1 and 2):
Kishanth学生问了我一个关于8分写作的语法评分标准的问题（同时适用短作文和长作文）：

uses a wide range of structures
语法结构使用广泛
the majority of sentences are error-free
大部分语句无误

Here's the problem with these two points:
对以上两点有这样一个问题：

When you try to use a wide range of grammatical structures, you risk making more mistakes (errors). But to reduce the number of mistakes, you might have to simplify your sentences.
使用多种语法结构会面临出更多错的风险。但为了少出错，可能不得不使用简单的句子。

So what should you do?
我该怎么做？

My advice is this: Forget about the 'wide range of structures' point. If all of your focus is on using complex grammar, you'll probably do something worse than just make mistakes; you'll probably forget to answer the question properly. The people who worry most about grammar usually neglect task response, coherence and vocabulary.
我的建议是：别管“语法结构使用广泛”。如果你把全部注意力放在使用复杂的语法上，你可能会遇到比犯错更糟的事。你可能忘了正确回答问题。最担心语法的人往往忽略了任务完成情况、连贯和词汇。

For me, grammar is the least important criterion to worry about. I tell students to focus on the other 75% of the scoring system: task response, coherence and vocabulary. However, if you want my tip for improving your grammar score, I'd say that it's better to focus on reducing errors. I think examiners notice errors more than they notice grammatical range, and if you write a mix of short and long sentences, you'll probably fulfil the 'wide range of structures' requirement without realising it.
对我而言，语法是最不需要担心的评分标准。我告诉学生，把心思放在剩下的75%评分上：任务完成情况、连贯和词汇。然而，如果你想知道我的提高语法分数的技巧，我建议你把重点放在减少错误上。我认为，相比语法范围，考官对错误更为在意。而且，如果你能混合运用长句和短句，你可能没发现自己其实已经符合了“语法结构使用广泛”这一标准。