Students have very different approaches to drafting their essays. Some use a 'linear' approach, starting at the introduction and writing sequentially through to the conclusion. Others prefer a more 'recursive' approach where they work on one section for a time, move on to another part of the essay, and then return to the earlier section. We would not want to argue for any single approach. However there are several techniques worth employing.
One is to have a fairly clear notion of the structure of the essay before you do too much drafting. (Have a look to see how the early provisional plan has been developed into a final elaborated plan.) You will find that the flow of words will come more easily if you know in advance how the different parts of the essay are likely to hang together.
Another technique is to commit yourself to an introduction as early as possible. In the introduction, you should be looking to outline to the reader i) the structure of the essay and ii) your main argument. Your draft introduction will provide an initial anchor for the rest of the piece, even if later you find that you need to modify it.