Raghu,
I think you should not measure your prepration by the no. of essays you practice,but most important is to get the basics right.If you can write one essay and score 6 then whatever may happen(till you are not doing it delebrately)your score will always be in the range of 5-6.(That's my experience..)
Therefore, the most important points which I have learned ,and are applicable for any essay are :-
-Read the topic carefully ( Sometimes it may have a hidden clue or meaning)..Pay attention to words like support,Explain etc.
-Make a structured planned approach. (But,watch the time as too much time spent on planning will mean less time for writing...a mistake which I made and thus lost valuable 10 marks on the overall score).
-I really benifitted from the advice of erin that in case we have to take a stand in an essay it would be much better and also sensible to make the most obvious choice...as it is more easy to justify taking the time constraint into consideration.For e.g. if we are asked which is more benificial war or peace ?,the answer is obvious but then if I say war is more beneficial it cannot be said that I am wrong (as, it is a matter of opinion) but then I would have to give some solid logical arguments with supporting examples which may be possible but not easy in the 30 minutes.
The essay which I got in the exam is a good example of the same i.e. "The doctorine of the obvious".Honestly,I want to build a swimming pool on the land I get and invite all my friends and have a good time but then my objective is to get a good score in TOEFL, therefore in the test I wrote that I want to build a house for my old parents and then expanded on the same giving justfications and examples.It is more easier to support and above all looks "politically" correct.
Hope this helps.
Sanjiv.