Probably my favorite abstract technique is panning. Essentially, you set the camera to a longer shutter speed and spin, zoom, and/or move the camera to get a blurred, streaked look. I love it.
One of the things that’s really fun [but ohmygosh, so hard] to do is move the camera at the same rate as your subject to make the subject sharp and the background blurred.
In this photo, my little brother was [not unusually] running around in his Robin costume. So I decided to make him run back and forth for about a half hour. This is the best result, and I’m rather pleased with it. : )