Not all sharks hunt the same prey since many live in different habitats with different marine animals. Although, all sharks are meat eaters so most of their diets consist of fish, crustaceans, mollusks, plankton, krill, marine mammals, and sometimes other sharks. Sharks at the top of the food chain tend to eat larger animals such as seals and dolphins. Smaller sharks at the bottom of the food chain tend to be bottom feeders and eat anything on the seafloor. Like the English language, there are exceptions. For example, the largest shark today, the Whale Shark, feed on microscopic animals like krill.
Another part of any organism's diet is the amount of food they eat. Again, this answer varies depending on what type of shark it is. Some sharks can eat a huge meal then not have to eat again for weeks because they can survive on oil that is stored in their liver. They will have the instinct to eat again when the amount of oil is low. Sharks also don't have to eat as much because they are cold-blooded so their circulation slows and they burn energy at a slower rate when they go without eating. Since sharks have poor eyesight, they use other abilities such as their keen sense of smell to find their next meal.