[CyberED]

I'm assuming that you have an idea of what interests you and that you are shooting for a PhD or masters by research.

Research your topic of interest on Google Scholar. Read widely to identify who are doing comparable work.

Write a research proposal and send to the professors who are doing and supervising such work. You need to be very passionate about your topic in order to sustain you through 3-5 years of grad school. Of course, what you write your thesis on won't resemble your research proposal. That's just the way it is. You discover so much as you dig deeper and deeper into your chosen area.