Unless you are already getting very high marks for your essays, it is likely that your writing has not been sufficiently organized from the reader's point of view. This is a very easy mistake to fall into, because of the lack of actual contact with the audience which is basic to the writing situation. The only way of making up for this is to anticipate the needs of your readers by imagining an audience - the more accurately you can do this, the better your writing will become. Marking feedback is designed to help you in this process of imagining and anticipating possible audience responses for your next essay.
It is hard work to incorporate anticipations of your audience's response into your writing in the form of cues for your reader, but your writing is much more likely to be seen as having a clear structure if you make the effort to do so. If you are finding it very easy to write an essay, you should ask yourself whether you are paying enough attention to issues of design for a reader, since it is proverbial that "easy writing makes hard reading".
One important way of making your essays more reader-orientated is to ask yourself the question of what the reader is going to get out of your writing (ie the so what question). Viewing the essay as an exercise in persuading your reader of something, rather than as merely a repetition of points your reader already knows will make it more interesting to read, because you are supplying a strong motivation for the material it contains. For this reason, it can be a good idea to find an unexpected angle on the question.