"There is never only one way of doing it. Some arguments will suit a strong simple line through the essay, while others will benefit from changes in direction, things held in parallel, and so on. The key thing is that the structure doesn't get in the way of you saying what you want to say."
It is common to have a few points which are difficult to place in your plan. Sometimes these are irrelevant to the essay question, in which case they should be discarded. It can be difficult to reject material which you have spent time in gathering and thinking about, but it may well make for a better essay, as it will allow you to explore more relevant points in greater depth. Such work is never wasted; your wider reading can be discussed further in supervisions or may contribute to exams. However, there is some flexibility in how strictly you define whether something is relevant to your essay - some supervisors may prefer a looser approach in exploring the question, especially in the first year.
You may find that some points could be placed in more than one section. In this case, the point may be a thread running throughout the argument, and could be touched on each time it arises, noting how it impacts on the point currently being discussed. If you intend to raise it only once, you will need to decide when the point should first be introduced. If later points are dependent on it, then it should of course be made early in the essay. You can refer forward or backwards to a point, so you need not deal with it in depth every time you mention it (see the section on Connectives for more information).
Finding the logical starting point can be a challenge, like finding the end of a tangled ball of string. However, unlike a ball of string, there is always more than one possible way to start - you could experiment with several before deciding. One of the advantages of planning is that you can experiment with different ways of structuring the material without writing it out longhand, which is more time-consuming and may not be possible in the time-pressured context of a weekly supervision or exam.