A good thesis depends on good research questions. When you selected the topic you like try to find problems related to that topic and form appropriate questions. Properly formed analytical questions would make your research logical and innovative. Try to avoid descriptive sub questions and think of how you could incorporate your theoretical framework into them. Before thinking of questions familiarize yourself with the main concepts involved in your problematic and make a list of them. Such tactics will help to structure your ideas and find right questions. Do not write more than three questions, remember that you are just a student and your work should not be too extensive.
A very important piece of advice on writing a good research will be about time management. When you start working on your thesis it is extremely important to calculate how much time you need to finish everything on time. Good and responsible supervisors who care about their reputation will help you setting deadlines and pre-defence, however majority of them do not do that. Therefore, do not expect your supervisor or department to take care of you when it comes to managing time. After submitting a research proposal, selecting appropriate methodology, arguments, theoretical framework and literature make a plan of your activities. Plan your work step-by-step and do not leave everything till the end because you will just not manage to write around 20 000 words in few weeks.
Secondly, successful paper depends on what theoretical framework you are using. Many students do not receive good marks for their dissertation simply because they forget to include theoretical framework or cannot explain why they selected their theoretical approach. The selection of your theoretical framework should be based on which faculty you are studying. For example, if you are political scientist or study international relations there are few meta-theories which basically explain all fenomena in the field. These are realism, liberalism, constructivism and structuralism. All fields of science have different approaches to researching problems which exist within their focus so before starting your dissertation make sure you know all of them.
Successful paper requires a thorough selection of methodology and methods. The quality of your research may sometimes only depend on this aspect. If you have selected quantitative methods to solve your research puzzle and do not really understand mathematics and statistics your chances to fail increase. Always do what you are confident in. If you are a social scientist qualitative methods may suit you more and will be easier to perform. Majority of students are using discourse analysis method when writing their dissertation. This method is very general and definitely useful but if you do not add other methods such as interviewing or conducting surveys your grade would be lower.
A good thesis has an added value. However, this part is considered to be the most complicated one. Since you are a student in your final years you are probably not able to come up with new ideas and innovative approaches to solving complicated issues on which so many qualified researchers and doctors are working on. But it is actually not the case. No one is expecting to actually create a new knowledge from you. You are a student and professors understand your background and capabilities. Therefore, do not think of solving big problems but rather select something small and under researched. Look at the number of publications and books in the field you are interested in. However, do not select topics which are too under researched. Remember that you have to use many sources and literature to write a successful thesis.