It depends on the beach you're at, the previous high tide, the current and winds that were in play, and the way the sand is lying on any given day. Sometimes the goodies can be up higher in the wet sand. Sometimes they can be down at the shell-crush area. And sometimes they can be further out to where you still can't get to them without going deep. At our beach I have a lot of luck in the wet sand at low tide, between the water's edge and maybe about half way up to the dry sand line. Like pretty much in the middle of the wet sand area. But if that's not producing then I will go a little higher to see if the targets migrated up or I'll try lower, down in the water, to see if there's more down there. I run a kind of an "S" pattern in the wet sand and try to go slow and be patient until I hit a target or two. Then it's a matter of following the "line" of targets, wherever that may lead. Most of the time you can find patterns of distribution, maybe even by weight...follow the dimes to the nickels to the quarters to the gold rings, for example. Sometimes it's just hit and miss. And very definitely you can have a certain area of the beach that is DEAD as far as targets today but after another tide cycle or two the same area can be loaded with targets. You have to also watch for cuts and beach erosion, where you can see that a significant amount of sand has moved around. This is where you can often hit a "honey hole" of targets. Of course there are a lot more points to ponder and many a book has been written on the subject so perhaps you might want to check one or two out.
Here's a link to a Google search using the term "beach metal detecting". I see a few good links there that might help too.
http://www.google.com/search?hl=en&q=beach+metal+detecting
