Always cover your holes. Always. Just fill the hole up with sand
Don’t detect when the beach is crowded. We already have a bad rep with the public. People do not like to see us detecting around their kids at noon on a crowded Saturday. Go early in the morning when those people are asleep or hunt in an uncrowded area if you must hunt at peak beach times.
Don’t break the law.
Don’t leave trash. Take those soda cans with you, don’t leave them in the ground. I usually throw my garbage away after each hunt but some guys save it. Even if it's junk just please take it with you.
Be nice when people approach you. They will approach you. Most of them are really nice and curious about detecting. If someone is bothering you or you can tell they are trouble just walk away and hunt somewhere else. This is another reason why hunting early in the morning is a good time to hunt.
If kids are following you give them a penny you find and be nice. You may make a future detectorist out of them.
Don’t dig around people laying/sitting. If someone is laying out do not detect a few feet from them. Give people their space.
Respect the beach. If we don’t we will lose our privilege to detect.
Know the area. Is it safe? What is crime like? In these cases it may be good to have a hunting buddy.
Don't leave your detector in a hot car, it can ruin the electronics
Be healthy. Make sure you are protected from the sun, have enough water, etc.
If jewelry is marked, try to return it (I realize this is difficult but at least check craigslist lost and found)