Normally, we're taught that one of the basic rules of composition is to have a strong subject; in fact, that's almost taken as a given most of the time. However, compositions without a dominant or obvious subject can also make for great images, as this interesting video discusses.
Jackson Pollock has always been my favorite painter, partially because his works refuse easy readings, requiring you to stare at them, taking in both every part and the whole simultaneously. With some thought, I think that concept can transfer to photos as well, as Ben Horne discusses in this interesting video. As he mentions, compositions that capture a certain controlled chaos work particularly well. I also think that one might be able to successfully employ the concept with aerial photos. While drone photos can certainly have prominent subjects, I find that many of my favorite shots simply show off some sort of geometry or interesting symmetry that is afforded by the elevated perspective. While the controlled chaos Horne mentions works, minimalistic compositions also benefit from such an approach. Even if it's not your cup of tea, it's a good exercise to expand your compositional eye. Give it a try!