These can be caused by oversight or carelessness during the drafting process. While it is quite natural that these errors occur when drafting, you should check your final work to ensure it is well presented. Many, but not all, of these errors concern wordprocessed work, rather than handwritten.
Typographical errors, or ‘typos’, can occur when you are typing quickly but not accurately. You may miss a key or hit the wrong one, or in the wrong order. Some typos are clearly typing errors rather than spelling mistakes (common ones include ‘teh’ instead of ’the’, ‘ahve’ instead of ‘have’, or running two wordstogether). Your word processor’s spellchecker will pick most of these up and automatically correct them. You should double check, as some typos can also be real words, and this may look as if you don’t know which is the right version. A common example might be ‘form’ instead of ‘from’.
Inconsistencies might include varying use of capital letters, variant spellings (especially switching between US and British English), use of font effects such as bold or italics for subheadings or book and journal titles etc., formatting issues such as margins, indents and line breaks, and presentation of references. Once you have established a convention for presentation or spelling, you should make sure you stick to it.
Omitted elements. You should make sure there is nothing missing, such as page numbers or incomplete references.
Accidental additions or repetitions can result from typing errors if you are coping from a text in front of you, or from cut-and-pasting text.
Adherence to house style. There may be a particular style in which your supervisor or the Faculty wishes your work to be presented (e.g. font and font size, line spacing). You should make sure you stick to it. You should also make sure there are no unfortunate page breaks, such as a subheading at the bottom of a page.
These errors can be difficult to spot in your own work, as you often read what you intended to write, rather than what is actually on the page. It is easier to see errors once you have put the work aside for a while, but you may not have the luxury of enough time in a weekly supervision essay. One strategy is to read your work backwards, a word at a time, so that you are not distracted by the meaning or content, but can focus only on the words individually. Some aspects of presentation, such as line spacing, page numbers or font can be set as defaults on your word processor. Making a personalized checklist of other presentation conventions to check for, such as capitalization, can also be helpful, and fairly quick to do.