Now I m studying in iBT Toefl course. For me, it's very difficult - how to write essay in short time, how to issue idea and structure.
Well.... follow the four para structure; Introduction, 2 body paras and Conclusion.
Introduction - Introduce the topic + state your opinion about the argument
Body para 1; Give your first reason for your opinion + support it with a specific example
Body para 2; Second reason + example
Conclusion; Sum up everything you said about and re-instate your opinion.
There are many good essays you find under TOEFL... Follow their structure :)