Grad open houses can be a good excuse to meet with a POI. "Hi Dr. So and So. I'm interested in your program and I am going to attend the open house. I noticed that you do XYZ work. I'm interested in XY work, and I was wondering if you'd have some time that day to meet." Something like that. Obviously the research interest needs to make sense, but it can be an easy way to make a connection. Larger conferences can be hit and miss, but niche conferences can be great networking opportunities. Having a CV available is always a good idea...whether you are at a conference, open house, etc. I always carry business cards too, a good hold-over habit from my days in the biz world.