TOEFL iBT Independent Writing Structure.
The objective of the TOEFL independent writing essay is to assess your ability to clearly and logically express your ideas in English. To do this well you not only need to be able to write English at the sentence and paragraph level but also at the essay level. A TOEFL independent writing essay should be at least four paragraphs long (five is probably better, but six is probably too many). These 4 or 5 paragraphs should be divided into an introduction, a body, and a conclusion.The basic structure of a TOEFL independent writing essay should look like this -
Introduction
Body Paragraph 1
Body Paragraph 2
Body Paragraph 3
Conclusion

Let's look at what we need in each of these different parts of the essay.
Introduction
In the introduction we need three things: background information, hints at essay development, thesis statement.
1. Background information is some kind of general statement about the topic of the essay. It does not actually answer the question posed in the essay topic, but gives the reader the impression that you (the writer) know about the topic, have thought about the topic or have experience of the topic.
For example, if you are asked to write an essay on the topic 'What is the most important animal in your country?', your background information might be something like "The relationship between human beings and animals is a very long one indeed. For tens of thousands of years animals have served as a source of food, labor, and companionship for humanity. Even in the technology-driven 21st century, animals still perform these roles."
2.The hints at essay development should give the reader some idea of what you are going to talk about in your essay. DO NOT say things like 'I have three reasons', or 'there are two reasons for this' in your introduction. The hints at essay development will tell me your reasons. For example, if you are asked to write an essay on the topic 'What is the most important animal in your country?' and you write, "The cow provides us with meat, milk and leather; three products we are unable to manufacture synthetically" , that would be your hints at essay development.
3. The thesis statement is your position on the topic. For example, if you are asked to write an essay on the topic 'What is the most important animal in your country?' and you choose to say, "In my opinion, the cow is the most important animal in my country.", that is your thesis statement.

The standard order in an Introduction is -
1.background information
2.hints at essay development
3.thesis statement
although
1.background information
3.thesis statement
2.hints at essay development
is also possible and often easier to write.  Let's see how they go together using the examples above. First using 1,2,3 order.
The relationship between human beings and animals is a very long one indeed. For tens of thousands of years animals have served as a source of food, labor, and companionship for humanity. Even in the technology-driven 21st century, animals still perform these roles. This importance of animals to human society is most easily seen in the cow. It provides us with meat, milk and leather; three products we are unable to manufacture synthetically. In my opinion, the cow is the most important animal in my country.
Now using 1,3,2 order.
The relationship between human beings and animals is a very long one indeed. For tens of thousands of years animals have served as a source of food, labor, and companionship for humanity. Even in the technology-driven 21st century, animals still perform these roles. This importance of animals to human society is most easily seen in the cow, and I firmly believe that this creature is the most important animal in my country. It provides us with, with meat, milk and leather; three products we are unable to manufacture synthetically. 
Body Paragraph 1
In each body paragraph we explain or discuss one of the hints at essay development that we mentioned in the introduction. This becomes the topic of the paragraph. What we actually need in each body paragraph is -
Topic sentence (this tells the reader what the paragraph is about)
Supporting sentences (these support and explain what is stated in the topic sentence)
For example, using one of the hints at essay development mentioned above, you might write a topic sentence like "Firstly, humans have, for millennia, raised cows for the milk they produce." , Next you would write some supporting sentences that make the reader realise that what you said in your topic sentence  is correct. For example
"This liquid is an essential part of the human diet. For children it is a natural follower to the mother’s milk they drink when they are babies. As they grow older the calcium contained in milk helps them develop strong teeth and bones. For adults, too, milk features prominently in most people’s diet. Many find it difficult to drink coffee or tea without milk, and cereal, that commonly consumed breakfast dish, simply cannot be eaten without milk."
Body Paragraph 2
The same structure as Body Paragraph 1
       Firstly, humans have, for millennia, raised cows for the milk they produce. This liquid is an essential part of the human diet. For children it is a natural follower to the mother’s milk they drink when they are babies. As they grow older the calcium contained in milk helps them develop strong teeth and bones. For adults, too, milk features prominently in most people’s diet. Many find it difficult to drink coffee or tea without milk, and cereal, that commonly consumed breakfast dish, simply cannot be eaten without milk.
Body Paragraph 3
The same structure as Body Paragraph 1
       Finally, though beef and milk are the products most people associate with cows, we must not forget leather. Although this material can be obtained from other animals, the most common kind of leather is produced using the hides of cows. It is a product used in the manufacture of bags, gloves, clothing and shoes. Of these, it is in the manufacture of shoes that cow leather is most important. Leather is not the only material used in the producing footwear, canvas and plastic also being common, but the leather is the strongest and the most comfortable, especially for formal or work shoes. Everyone in the developed world probably has at least one pair of these and the overwhelming majority will be made of leather.
Conclusion
In the conclusion we need to tie everything together by summarizing the main points of the essay again. We can most easily do this by restatement. When we do this we are basically repeating the hints at essay development and thesis statement that we wrote in the introduction. Be very careful that you do not just copy the same words. You MUST restate them - that is use different words. For example, in the introduction I said 'they provide us with milk', in the topic sentence of body paragraph 1, I said 'the milk they produce' and in the conclusion I might say 'we obtain nourishment from its milk'.
 
Let's look at the completed essay without the explanation.
Introduction

       The relationship between human beings and animals is a very long one indeed. For tens of thousands of years animals have served as a source of food, labor, and companionship for humanity. Even in the technology-driven 21st century, animals still perform these roles. This importance of animals to human society is most easily seen in the cow. It provides us with meat, milk and leather; three products we are unable to manufacture synthetically. In my opinion, the cow is the most important animal in my country.

Body Paragraph 1

       Firstly, humans have, for millennia, raised cows for the milk they produce. This liquid is an essential part of the human diet. For children it is a natural follower to the mother’s milk they drink when they are babies. As they grow older the calcium contained in milk helps them develop strong teeth and bones. For adults, too, milk features prominently in most people’s diet. Many find it difficult to drink coffee or tea without milk, and cereal, that commonly consumed breakfast dish, simply cannot be eaten without milk.
Body Paragraph 2

       A further source of nourishment we derive from our bovine friends is beef. This has been an important source of protein for many societies since the early days of stock-raising. In recent years, the globalization of economic activity and particularly that of agriculture has led to beef penetrating the diets of those whose societies traditionally found other sources of protein. As fish stocks decline due to dangerous overfishing, beef seems certain to become an even more important part of many people’s daily consumption. Although there are alternative meat sources, such as pork and chicken, beef has greater appeal for many people.

Body Paragraph 3

       Finally, though beef and milk are the products most people associate with cows, we must not forget leather. Although this material can be obtained from other animals, the most common kind of leather is produced using the hides of cows. It is a product used in the manufacture of bags, gloves, clothing and shoes. Of these, it is in the manufacture of shoes that cow leather is most important. Leather is not the only material used in the producing footwear, canvas and plastic also being common, but the leather is the strongest and the most comfortable, especially for formal or work shoes. Everyone in the developed world probably has at least one pair of these and the overwhelming majority will be made of leather.

Conclusion
       In conclusion, the benefits which the cow offers to modern society are irreplaceable. We obtain important nourishment from its meat and its milk, and our feet are comfortably protected by its leather.  A world without steaks, without cool glasses of milk, and with our feet encased in plastic would not be such a pleasant one. It is the cow that stands between us and such a world; consequently it is undoubtedly the most important animal in my country. (479 words)

Important Points
1) When we move from one paragraph to the next we need to make a smooth transition the the next paragraph. The easiest way to do this is to use words such as First, Secondly, Finally and In conclusion. There are many transition words,  (for example look at paragraph 2) but these are the easiest?
Can you think of any other words or phrases you could use to move from paragraph to the next in the essay above?
2) Try to use different words when you change your hints at essay development into topic sentences, and then again when you restate in the conclusion. You need to think about synonyms.
Can you see any  synonyms in the essay above?
3) You need linking words to hold your essay together.
Look at the word 'too' in body paragraph 1. They tell the reader that the writer is giving another example of milk being an essential part of the human diet.
Can you see any other linking words?

Go on to sample essay 1