When writing you thesis try to develop your opinion about the material and identify the reasons why you have that opinion. In most cases the thesis statement will be one sentence and it will form the focus for the whole paper. Each paragraph will focus on one of your reasons from the thesis and each paragraph will end with an explanation of how the proof supports the opinion in the thesis. Needless to say, this makes the thesis the most important sentence in the paper. As you are no doubt aware, the drafting stage is the actual writing of the piece.
Some people just sit down and write a piece.
In the drafting stage the focus should be placed on the conventions of writing. The idea here is to take the ideas from the brainstorming stage and work them into complete sentences and paragraphs. This will be the material you found in your research that you feel supports the point you are trying to make. In the vast majority of cases this will be a direct reference or quote from an important source. Take time to explain how the proof you have provided backs up the point you presented in the topic sentence and how it helps to support the overall opinion presented in the thesis.