Organic shapes are a favorite of mine. I like to play with what I believe are built-in pattern recognition algorithms we all have wired into our brains.
More generally, I target a range of abstraction that is between a what I call a strictly representational picture (for example, a pretty color postcard) and a totally abstract image where the viewer has no idea what the actual object being photographed is. In my first serious one-person photo show in 1981, which was very intentionally a market test of what viewers reacted to, I had a full range between those two extremes. Only artists liked the totally abstract, and the strictly representational photos were not considered art.
Abstraction and art seem to be connected to what makes us human. While I strive to capture the literal details of reality in my photographs, I also hope to have the forms trigger thoughts and emotions that go beyond what is actually pictured.