Universities that expect their students to write dissertations follow only one rule, which is to make rules no matter what! And when it comes to you, your safest bet is to follow these rules rather than risking failure and imminent doom.
If you want to get it right at the first attempt, make sure you make an impressive proposal for your dissertation. Your dissertation proposal should talk about what you plan to demonstrate through the dissertation.
The proposal document is the key for the guide to understand what your genius mind wants to convey, so make sure it actually makes you look like a genius because the dissertation proposal is greatly responsible for the acceptance or the rejection of the dissertation as a whole, so unless you need more time to decide the actual dissertation topic, get your proposal document right.
When you have finally made up your mind about the topic for the dissertation, writing the proposal is the next big step for you. You can choose to write the proposal on your own, without taking any help from anywhere, because you know it all.
Or search for the answers on the web and risk putting in hours for something that might or might not be the right way to do it, because remember the proposal found on the net are the ones written by students like you.
Or you can choose to take help from an expert or a professional who can show you the right techniques for writing a good dissertation proposal because taking a safe path to writing the dissertation proposal is the first battle won. When you know what you propose for sure, you can see the entire dissertation become a cake walk.