When writing at University level you are expected to have checked, re-checked, edited and proofed your assignment several times.
For the proofing and editing process to be particularly rigorous and effective you should focus on a different aspect of your writing each time you read through your work. Consider some of the questions below while reading your essay:
Does my essay have a beginning, a middle and an end?, Does my introduction prepare the readers for what they are going to read?, Does my conclusion link back to what I have said?, Is my essay balanced? (10-20% introduction, 10-20% conclusion, the rest is main body)
Are my arguments clear?, Are my arguments presented logically?, Do I have proof for what I am claiming?
Use of sources:
Am I using good sources?, Am I using the sources well?, Am I critical in my use of the sources?
Referencing and bibliography:
Have I provided all the details required?, Have I used quotation marks?, Have I provided page numbers with direct quotations?, Are my references consistent?, Am I using one style only within the Bibliography?, Is my bibliography in alphabetic order?
Is my writing formal or informal?, Have I made any spelling errors?, Is my language consistent (American English vs. British English)?, Are there any grammatical mistakes?