Writing essays can essentially be split up into a few basic parts.
Decide what you are writing about, what you want to say, and who the essay is going to be read by (generally a teacher, professor, examiner etc.).
Plan the essay – this will ordinarily involve deciding exactly how your essay will be written, i.e. which paragraph will be devoted to which part of your argument etc.
E.g. Discuss the effects of Creatine monohydrate on muscle growth
Introduction: This should outline all the points you intend to cover in the essay (all the paragraph titles), as well as a brief summation of what you will conclude. Essentially giving a short outline of your essay/argument in the introduction helps to add cohesion.
Paragraph 1: Should begin with a more in-depth commentary of a subject already highlighted in the introduction. E.g. Early understanding of Creatine. Once the subject has been made clear, you should then make obvious its relevance to the essay title/question. For example: “Creatine was discovered as an organic constituent of meat some time in the early 1800s. Later in the 1800s, Cr was consistently detected in muscle tissue extracted from various mammals” could lead into “Around this time a substance called creatinine (Crn) was detected in urine, and later determined to be a breakdown product of Cr. Phosphocreatine (PCr) was first isolated from muscle tissue in 1927 and found to play an important role in the transfer of energy.”
Once you have planned out the essay you can then write it. This should be a simple task of writing out what is already in front of you in plan format. Obviously elaboration and a more formal writing style will be required to turn a plan into an essay, however, with the basic points in front of you writing the essay becomes much easier.
Finally, once the essay has been written, you ought to proofread it to check it makes sense in all parts – e.g. it answers the question posed by the title, each paragraph follows a specific theme, there are no spelling or grammatical errors and so on. It may be a good idea to have someone else proofread your work too, as they may be able to spot mistakes you cannot.
If writing an essay under timed conditions a detailed plan may not be possible; instead it is permissible to simply and briefly outline the paragraph titles to give some structure to your essay before you write it.
Indeed, when writing essays under timed conditions you must make sure that you give yourself enough time to answer all questions sufficiently. E.g. an exam that is split up into one 30 mark question and one 40 mark question in 2 hours, ought to be split roughly into 50 minutes to answer question one and 70 to answer question 2, including no more than 5-10 minutes planning time.