To find fossils, we first need to understand what fossils look like. Fossils formed from the fossilization of ancient organisms, such as animal and plant remains, are not particularly unusual in appearance. For example, plant fossils look just like plant roots, stems, and leaves, but they are fossilized. Animal fossils are more complex. Some preserve their shells (such as mussel shells and snail shells), hard bodies (such as insects), or only their hard bones (such as reptiles and mammals), but they are still easy to identify. In addition, we need to understand which geological layers contain fossils. Fossils are not found in volcanic rocks, but are typically preserved only in sedimentary rocks. However, different types of sedimentary rocks also have very different fossil burial conditions. For example, coarse sandstone, conglomerate, and dolomite generally do not contain fossils, because their rock structures and sedimentary environments are not conducive to fossil preservation, or their formation environments are not suitable for the survival of organisms. Only rocks with structures and sedimentary environments suitable for the growth of organisms and the preservation of fossils, such as limestone, marl, claystone, sandy claystone, siltstone, and shale, are suitable. Fossils from different geological periods are also completely different. For example, to find trilobites, it is best to look for them in Cambrian strata (540 million to 500 million years ago). There are also trilobite fossils in Ordovician and Silurian strata, but the younger the strata, the fewer trilobites there are. If you want to find plant fossils, you must look for them in terrestrial strata, especially in layers with a high organic matter content, such as coal strata. Dinosaur fossils can be found in Mesozoic terrestrial strata. In other words, we need to have a general understanding of what fossils might exist in what geological periods, and whether the fossils belong to marine or terrestrial environments. Of course, it's impossible to find marine organisms in terrestrial strata.
Geological conditions often vary greatly. Different places, different geological periods, and different rocks are often very different. However, as long as we search more and summarize our experiences, we can find patterns in them. For example, in the Early Cretaceous (more than 100 million years ago) terrestrial strata in western Liaoning, China, important fossils such as birds, insects, plants, freshwater fish, and small dinosaurs and pterosaurs are often found in thin layers of dark gray and gray-white claystone. Local villagers often help paleontologists find these fossils, and over time, they have learned where and at what layers they can find what fossils, and even what fossils can be found several meters underground. As the saying goes, "Practice makes perfect", which is very true. In some areas, there are very few fossils, so finding fossils requires patience. If you can't find fossils in a stratum for a long time, you might as well look further along the direction of the stratum's extension. The harder it is to find, the more unexpected rewards you will get if you find fossils there.
It's worth mentioning that there are fake fossils in some rock cracks. They look a bit like plant tree trunks and leaves, but if you look at them carefully with a magnifying glass, you can see that they are not tree trunk fossils or leaf fossils at all, but some black manganese deposits distributed along the rock fracture surfaces.