If you were unsure of some answers, go back and reconsider them. There is little research on testwiseness as it applies to essay exams. This is because there are relatively few clues to take advantage of in the essay format. Time is usually a crucial factor on essay tests. Usually it's a good idea to answer the questions that you know best first.
Many students fail to appreciate the importance of good organization in their essay responses.
If your instructor can't follow where you are going with your answers, you won't get many points. Test essays are often poorly organized because students feel pressured for time and plunge into answering questions without any planning. It's a good idea to spend a minute getting organized first. Also, many examiners appreciate it if you make your organization quite explicit by using headings or by numbering the points you're making. In writing essays, the trick is to be concise while being complete.