My topic was an extension of what I did in honours, and in the year after honours while I was a research assistant (so I've been doing it for - nearly 6 years!) - to sum it up it's looking at bacterial resistance and non-antibiotic antimicrobials (sounds way more fancy than it is, but you'll have to excuse me as I don't want to go into more detail on the web as it's a small field of research and you never know who could stumble across this forum and discover my fertility issues!).
Is your topic completely new to you or do you have some background in it? You'd be surprised how many things you come up with during the process. Also, the important thing to remember is that you don't have to have a complete story - I always worried about that - and as one of my supervisors says, "No result is still a result" ha ha.