Do your research first
If you do your research first and make notes then you will not be surprised by that stunning piece of evidence that makes you change the focus of your dissertation. Ideally, you find this piece of information during the early planning phase and not when you are half way through your dissertation and have to change it all back again.
Where you given a topic?
If you were then you can research the title and the topic and figure out roughly what your professor/teacher wants from you. If you are able to pick your own topic then there is a middle ground you can pick. You do not want to be too cliché, or pick a topic that is overdone because your teacher probably will not finish your dissertation and just give you a bland boilerplate grade. On the other hand, you do not want to be too creative because your professor/teacher may mark you down for fear of having to justify why he or she gave you the higher mark to an administrator. Also you should ask your professor how to structure a dissertation after you choose a topic.
Do not pick certain things for a topic
With a comparison dissertation this may be difficult. You can competently compare most things in the world, but to play it safe you should pick things that are not in a grey area. For example, if you were to compare and contrast the use of the word “inflammable” and “flammable” then you may be walking into a subjective-area nightmare. But, if you wanted to compare protestant Christianity with Catholic Christianity then you have clear boundaries you can comment upon (i.e. there are similarities, differences, and there are few gray areas to cause you problems).
Remember your professor has feelings and is human
Your professor has feelings, which means if you are comparing something that is a touchy subject, then he or she may be very inclined to mark you down. For example, your professor may have a wife that cannot use her legs, so your dissertation that compares stem cell research to playing god may upset your professor.
Also, remember that your professor is human, which means if you are rehashing a topic that he or she has seen hundreds of times, then do not be surprised if your professor is less than impressed by your insight. Plus, if there is a flexible word count, then go for concise over comprehensive.
Look at other peoples’ dissertations
You should not do this to copy other people. You should do it to see if you are on the right track. You can see if your work and your points are in line with theirs. You may have better points in your dissertation, or other people may have points that you can superimpose into your dissertation. Do not copy the work you see on the Internet because there is a good chance that A: it is wrong which is why it is published instead of being paid for, and B: other students will be copying it and you do not want to hand in a paper that looks very similar to the cheaters in your class.