Make a list of topics that interest you. Write down the idea that's been nagging at you, the question that keeps coming up, or the lightbulb that just went off 5 minutes ago. Recording your curiosity helps to free your mind to think about other things-- including the details of the original question! It also very often leads to additional questions, specific things you can look up, terms you might want to search for, a flaw in the idea, or alternatively, important implications. 

A list of ideas is a living document, something you are constantly refining and adding to. It may be messy or chaotic and have a lot of things in it. Or, it might just have one or two things you'd like to explore. 

Play around with mind mapping, sketching, diagramming, lists of lists, and any other online or offline technique that helps get things organized for you. 

Comment on some of the ideas you wrote down, if you're comfortable, and/or some of the results of jotting down your ideas. Did your mind go blank the first time? Did you decide the idea was good? bad? How did the act of jotting things down affect you or your thinking?