I do not often intentionally look for abstracts; many times it is a product of my attention wandering as I wait for something else to happen. I discovered a way of abstracting an image which works particularly well on images where there are a lot of subjects at a variety of distances from the camera. In other words, this technique wouldn't work very well for subjects on water or in the sky or open fields, that sort of thing. But, it does work well in shots of woods (and might also work on something like a crowd shot). The idea is to focus on something at the largest aperture of the lens so that the focus plane is very narrow and then, without changing focus (I will usually focus manually with this technique), search for something to frame in front of you that looks interesting - even if nothing is truly in focus. That is how I shot this image of woods which I consider to be one of my best abstracts. Notice that there is no blur due to motion in this image.
With the right forms, simply tilting the camera can produce an abstract image.
I'm not sure if I like this one or not. It was taken in a fern bed after the ferns themselves had died back, leaving the spore producing fronds.
Clouds are a good subject for abstract images. Some clouds are better than others.