For what purpose is this? If it's to judge your level, then it would be best if it reflects your current level (you want an accurate placement). It's a language school, after all - if you could write perfect Japanese you wouldn't need them.
General hints:
1) Use a dictionary which is for English to Japanese (most free online dictionaries are EDICT-based and it's really for Japanese to English). This will aid you in word choice.
2) Check the example sentences in the dictionary, not just the English meaning. Pay attention to what particles are used with which verbs. (It's not で住んでいる, for example)
3) Don't write in English then try to translate over. Use the sentence patterns/grammar you're confident to use in Japanese, even if that means simplifying what you can say, or breaking complicated sentences into two or more separate sentences, etc.