Just a few remarks and suggestions on top of what kani has already mentioned.
二〇一四年十二月十八日
天气:下雨也很冷
Make your description of the weather succinct. A one-worded description, such as '阴' usually suffices.圣诞节放假开始了,
The expression here is a little awkward. I'd recommend something along the lines of: "圣诞假期终于来临了!" Note the subtle difference between "放假" and "假期".每天我十一点左右起床。
I'd add something like "假期期间" before this for contextualisation.我起床的时候我吃早饭然后做数学和中文作业。
Again, the expression is a little awkward. I'd suggest something like: "早饭后就开始做数学和中文作业。做完然后我看电视或玩电脑游戏,有时候我出去跑步和运动。
Try: "做完作业后,我则开始看电视、玩电脑,有时还会出去跑步、运动。我和我的家人快要准备下周会去中国看我的住在中国的家人。
This sentence reads much better than the previous two. Only a few minor tweaks are needed: "下周,我和我的家人准备回国访亲。"我们要离开墨尔本在圣诞节的天, 先去香港,下飞机我们要呆两个小时然后山飞机去福州。
"我们将在圣诞节那天离开墨尔本,首先飞往香港,在香港逗留两个小时,然后从香港乘飞机前往福州。"我去中国我要更我的家很愉快的玩,我们去中国的时间是三个星期。
This sentence needs a little bit of work. Try: "我们策划在中国逗留三个星期,虽然时间短暂,可仍期望能跟家人在那里度过一个美好的假期!我妈妈绝太少时间。我们回来的时候只有一个星期(before)二〇一五年学校学期开始。
"我们将在开学的前一个星期返回墨尔本。我希望我努力学习所以我十二年纪我已经很好准备也很纪录。我知道我会拿到我想得到考分(if)我很努力也相信。
"我十分注重学习,所以已为十二年级做好了充分的准备。我相信,只要勤奋、自信,明年一定会取得理想的成绩!Edited version:
二〇一四年十二月十八日 阴
圣诞假期终于来临了!假期期间,我每天大约十一点钟起床,早饭后就开始做数学和中文作业。做完作业后,我则开始看电视、玩电脑,有时好会出去跑步、运动。下周,我和我的家人准备回国访亲。我们将在圣诞节那天离开墨尔本,首先飞往香港,在香港逗留两个小时,然后从香港乘飞机前往福州。我们策划在中国逗留三个星期,虽然时间短暂,可仍期望能跟家人在那里度过一个美好的假期!我们将在开学的前一个星期返回墨尔本。我十分注重学习,所以已为十二年级做好了充分的准备。我相信,只要勤奋、自信,明年一定会取得理想的成绩!
Overall, the content is great. There are, however, two main areas that need improvement:
1. Expression. Try to think in Chinese as you are writing a Chinese essay, rather than first establishing what you want to say in English, and then translating that into Chinese. I reckon the most efficient way to learn how to think like a Chinese person is to watch Chinese dramas. Listen carefully to see how the characters in those dramas construct their sentences, and try to emulate that when writing Chinese essays.
2. Structure. Although this is meant to be a diary entry, you don't want it to sound as though you are simply enumerating all the things that you normally do on the holidays. Try to structure your essay so that it has a mini introduction, at least two body paragraphs and then a conclusion. Your essay should have a focus. The first body paragraph should introduce what you intend for your essay to focus on, and the second body paragraph should zoom in on that topic of interest. Did you witness anything interesting? Anything humurous? Surely, there are more fascinating things to report than doing homework, and playing computer games. What exactly do you plan to do in Hong Kong? What about in mainland China? Having a logical structure can go a long way. It helps readers to understand exactly what your objective is in writing this diary entry. And the answer shouldn't be: because the teacher told me to do it!

Hope this helps! Best of luck next year!
