This is the first step and the starting point for your research. You don't need to have a specific research question in mind at this point – just a general topic that you want to explore. Make sure to choose something that interests you, that you are curious about, and that is relevant to your assignment.
Once you have decided on a topic, do background research. It will give you a good understanding of the scope of your topic: subtopics, key issues, etc. It will also help narrow your focus. It's possible that not a lot has been written on your topic, if that's the case, you can always choose another one.
To learn more, watch the short video below (create by the NCSU Libraries).
Narrowing your topic
You can narrow your topic by asking questions that start with "what", "how" or "why" (not necessary all of them though). For example, if your topic is earthworms, you can narrow it down by asking what effects do earthworms have on sugar maple saplings. There are many ways to narrow down a topic.
Common errors with research questions:
The question is too broad to be manageable.
If there are dozens of books and thousands of articles related to your research question, you need to narrow it down.
The question is too narrow
If you can answer with yes or no or if you can't find any literature related to your research question, you need to broaden it.
Research is a dynamic process. You will continue to modify your topic throughout your research process and it's completely normal. How you tweak your topic will depend upon whether there's too much or too little information or maybe you started observing your species in the Arboretum and something happens and a new interesting question emerges instead.
If you need help with your research question, feel free to: