Someone asked me how to come up with an idea for a dissertation the other day, and here’s how I responded:
…Most PhD programs in the US require students to take a couple of years of classes so they can better work out their academic interests and determine where they might best fit. It’s usually a process of socialization and indoctrination into the norms and expectations for the field as much as it is familiarization with content.
My cousin, however, is pursuing a PhD in Canada, and apparently they don’t have classes there, they just go straight to working on their thesis. I don’t know if they even have advisors.
So if your school format is more like the former system, I’d suggest you identify some general topics or themes you’re interested in, and begin to ask questions. Find classes that relate to these and build off of ideas you encounter.
If your school format is more the latter, then I’d suggest you think about a few key things:
1) The sorts of academics you’d like to model yourself after – namely active research professors and scholars you think are ideal
2) The types of research methods you find fitting – LIS is quite interdisciplinary, community informatics does well with ethnography and participatory action research, but these methodological frameworks would not be accepted in, say, bibliometrics and knowledge organization. Often researcher experience and personality type helps to determine what kind of research suits a person best.
3) In stride with what I suggested above, ask questions. Look at the “why’s” and the “how’s” behind social processes and work to link them to existing literature.
I think there’s a lot to be done in many areas. A few topics you might consider that I’ve always wished I could more deeply explore:

1. Cultural aspects of the digital divide and digital literacy; identifying and understanding social practices with technology that shape information sharing, expression and creation.
2. Positive impacts of values embedded in technologies. Critical pedagogy could be interlaced into the construction, interface, and teaching agendas behind initiatives like OLPC or other ICT4D efforts. While these technologies might bring negative corporately-driven values, like consumerism, they also bring other possibilities, such as student-driven learning or [more] gender equality.
3. Development and prototyping of media creation and analysis tools, like image annotation or collaborative video construction; exploration and best practices.
4. Fostering and encouraging social-justice and egalitarian thinking amongst videogame communities; the next steps of what to do after we find evidence of structural oppression in social media and games.