Three aspects: structure + vocabulary + making points.
======================================================
1. structure -- get familar with the conjuction words, and use difficult structures as much as possible. Because the marker likes them. It is also a way to convince them you really master the principle of the language. Compare the following two sentences:
A. I can improve my English by doing practice every day.
B. Only by doing practice every day, can I improve my English.
If you write the essay in a way as B, you will definitely get a higher score.
2. Vocabulary -- I suggest everyone, who want to get a score higher than 250, read the Vocabulary 5000 & 10000, authored by Taiwan's Liu Yi. I went through them many times.
3. Develop your points beforehand.
When I prepared for my Tofel, I went through all the 185 topics.
I classified the 185 topics into 10 groups. For the same group of topics, I can use the same points for the writing.
Take the example of two different TOEFL topics:
A. What characteristics you believe a good room mate must possess?
B. What are the traits that you think they are important in achieving your acamemic success or in your future career?
Obviously, you can use the same points ( at least 2) to write the above two essays. For example:
1. In my opinion, independent thinking is very important......
2. In addition,....
=======
All the best!
James
(I got 5.5 in my TWE)