In order to get an A, you need to show that you're comfortable using a range of different tenses, structures and vocabulary. By comfortable, they mean that you can use the tense accurately and several times throughout your written piece. Like any other subject, there will be an exact question; so just with English or History, you need to make sure that you're answering the question fully. For example, if the question is asking you to describe what school is like in the UK, you need to talk about a number of different things; uniform, exams, rules, food, etc. You also should make sure that there's nothing irrelevant in there, like what you like to do on the weekends. It is also important that your spelling and grammar is good, it doesn't need to be perfect (but that's what we'll work towards). We really need to make sure that you can spell all key terms correctly and that it's always clear what you're trying to say.