Summarize this article in one sentence.
The single best thing you can do to avoid ever seeing a shark is to simply pay attention to any and all safety information at the beach. Heed any posted signs and listen to the instructions of authority figures like lifeguards, beach patrol personnel, and park rangers. If certain activities like diving, kayaking, surfing, and so on are prevented in the water, don't do them. These rules exist to keep you safe. Sometimes, authorities make the decision that the easiest way to protect beachgoers is to keep them out of the water entirely. Though it can be disappointing to go to the beach and learn that it's been closed, don't try to disobey these rules. Their goal is not to ruin your good time, but to save lives. Most sharks hunt at these times and are naturally more active and aggressive when hunting. Stay out of the water at these times to avoid encountering a shark when it is likely to be hungry and actively searching for food. In addition, you are at a big disadvantage in the water when it's dark out. Since you have close to zero visibility, you are unable to see any sharks that you do come across. On the other hand, since sharks' other senses are more powerful than ours, they can navigate very well in the dark. Just as lack of visibility during dawn, dusk, and nighttime can make you extra-vulnerable to shark attacks, so too can water conditions that limit your visibility. As noted above, sharks have powerful senses besides their vision that can lead them to prey even when it's hard for them to see. Since humans lack these senses, we're much more likely to be taken by surprise by sharks in low-visibility water. Give yourself the best possible chance to see danger coming by swimming only in clear, non-turbulent water. Sharks are more likely to be where easy sources of food are. To keep your chances of encountering a shark at a minimum, stay far away from these places. Areas with commercial fishing activity can be especially dangerous since fishermen sometimes use pieces of chopped up fish as bait, which can inadvertently attract sharks. In general, flocks of diving sea birds are a good indicator that there is food in the water.  You'll also want to stay away from anywhere that nutrients, effluent, or waste products are discharged into the water (like, for instance, a sewage outlet that pours directly into the sea.) Not only is this likely to be a little healthier, but also safer, as the sharks are more likely to hang around such areas of water looking for food. If you are fishing, don't dump dead fish or fish pieces into the water. These make easy pickings for shark, which can detect blood at concentrations of as little as one part per million. Sharks that are big enough to pose a threat to humans generally stay in deeper waters off the coast. By staying in relatively shallow water and away from the "dropoff" area at the deep end of most beaches, you decrease the likelihood that you'll encounter a shark. Should you come across one, you'll still be able to get to safety on the shore easier.  In addition, you'll want to avoid the areas between sand bars — sharks can sometimes make their way into these narrow channels. Obviously, it can be hard to stay out of deeper water if you're doing activities like surfing or kayaking. In these cases, be sure to take all of the other precautions in this article to stay safe.

Summary:
Obey all posted warnings at the beach. Avoid swimming at dawn, dusk, or night. Avoid swimming in cloudy or murky water. Stay away from shark food sources. Stay near to the shore.