You have made the choice and you should be closer to settling on a worthwhile and achievable research topic. However, how would you find out whether your topic is actually worthwhile and achievable? Bear in mind that a basic understanding of your chosen research area is essential both to answer this question and to develop criteria for testing the quality of your topic - even if you may feel that you do not have very much time at your disposal.
What do you know about your topic? By getting to know your topic you will begin to learn what your topic is about - its context and content. In this way you not only begin activating the thinking process about your choice of this specific topic but also contributing to the research process that will ultimately lead to your dissertation or thesis. If it is a PhD topic that you are deciding upon and you are currently studying for an MA, then you may wish to use an MA essay or the dissertations as a way of beginning some preliminary work on the topic. Even as an undergraduate you may be able to choose subjects that will help.
If you have any time at your disposal, for example you have taken a gap year between BA and MA or MA and PhD, then you could begin to identify, access and consult some bibliographical resources. By doing preliminary research you will start reviewing the existing literature on your topic and related themes. Try to make a brief note of your findings.
By immersing yourself in the material, you start recognising terminology and authors that regularly appear, and discovering arguments related to your topic. You will begin to discover what your topic is all about and to identify different paths for future exploration as well as recognising issues which are over-researched. Draw up an initial plan for your literature review. This saves time later. Consult your potential future supervisor for key texts.
NB Your literature review will need to be continuous so that you remain aware of all the latest publications. In time you will be attending seminars and conferences and building up a network of critical (in many senses of the word!) colleagues who might like to comment on your topic/study. Get ready to run through your literature review again every so often to keep up-to-date!
Can you identify the main and related themes? Bear in mind that most topics are composites -they are made up of several themes which can also be studied and are also academically viable. For instance, if you thought about focusing on the works of a prolific author such as Camilo Castelo Branco you may consider limiting your topic by primary material, by theory, by theme, by approach, and so forth. It is essential to develop hierarchies around the topic of your choice. Through these you will determine the requirements of your main topic and related themes and start to improve your focus.