One of the problems is the word "essay" -- once we have the skill of "writing an essay" down it ends up being used in emails, in brochures, in business plans, in letters of request or recommendation -- the same skills we call "essay writing" in school is even used for short-form facebook posting through to long-form thesis or dissertation writing. But we call it an "essay" which makes it daunting. We could call it "Writing an Instruction Manual for a Game System". We could call it whatever -- it's just "good writing technique". Or if you will a "sandwich writing technique". Or best of all "writing for the reader".
An essay has to be organized in some way. You can't take random ideas and create an essay.
Think of an assignment to write an essay as if you're creating a game. The essay is like the introduction & tutorial for the game. How are you going to organize your intro/tutorial? First tell us the general idea of what it's about (subject/topic sentence) and the point of the game. Then let us know how the tutorial/rules are organized (i.e. movement/controls, character stats & skills, equipment, combat). Then get us ready for the tutorial in a summarizing sentence/transition sentence.
In the body paragraphs you tackle each topic of the so-called tutorial. In the first paragraph you introduce the idea of the controls of the game. Then you explain each detail. Then you get ready to transition to the next topic: character stats. That's when you're finally ready to go on to the next paragraph.
Thus each paragraph starts out introduction - details - transition. So now we introduce character stats, why they're important, how they're raised, etc. -- all the sub-topic details. When we're done, we need to move on so we introduce the next paragraph: equipment. The transition sentence is important so that the reader knows to change their mindset to expect something completely different--even if related.
So every paragraph will need both a main topic sentence -- this time about how equipment will help your character or enhance their actions in the game -- and a transition sentence. So you go on to mention important points such as identification, equipping, caring for, finding, buying, selling, etc. your equipment. Now we're done with this topic, and it's time to transition to the next idea: combat. A good example of a transition between equipment and combat is how improving your equipment can help in combat -- add some transition phrases to clue-in the reader, and you're ready to move on to the next paragraph.
So again, we introduce how important combat is to gain experience and progress, to gain loot, etc. in the game. We go on with the details of how to conduct combat, how to hurt or kill things, how to win & advance, level up, etc. When we're done, we're almost ready to conclude the tutorial, so we transition to the summary.
In conclusion, we state how we hope the advice has been helpful to them, and that they are about to embark on a great & amazing adventure. Thank you for sticking by us in this tutorial, and best of luck! That's the summary paragraph and thus the ending of your essay.
How does this structure apply to your essay?
Is your essay organized? Coherent? Introduced? Summarized? Is each paragraph also organized, coherent, introduced, summarized?
Do you need more help?
Do you see how the middle of this IS an essay, organized exactly as I outlined?
The essay doesn't jump between different topics -- it stays on-topic and focused. You don't want details on equipping items when you're talking about character stats or how to strike in combat, right? How do you manage the massive amount of information you want to convey to the player or reader without first organizing it into understandable, related, digestible chunks? Communication is not about your skill at expression in words and phrases -- but your skill in getting other people to see your meaning. If you are organized, they can see your meaning, and remember what you teach them better.