Well, there's mainly one simple rule in detecting. You find the spots where the greatest concentration of people go and then you go detect where they've been.
So find out where the tourist hot spots are...the places where people flock to the beaches, get in the water, and swim, snorkel, etc. That's where you'll find the goods. Now depending on the surf, tides, currents, etc. will depend on how much is IN the water and how much is in the wet sand and maybe in the dry sand where people lay out and stuff.
Here in Virginia Beach I've had a great deal of success hunting in the wet sand at the water's edge at low tide. And in the shallow water, like maybe knee to waist deep. The surf is rough and the water is dark, so doing a whole lot in water more than knee deep or so is tough here. Where you are, with sandy bottom, clear water, and often light surf I would think you might do better in the water where the greatest number of folks swim and snorkel and stuff. You really have to put the time in and learn YOUR beaches because there are no absolutes and beaches vary widely from one to the next. In the wet sand, look for cuts where the beach has been eroded. Look for concentrations of coins and follow the trail if you find one. When you find a hot area, grid-walk it and work it slow and methodically. In between the coins will be the gold. Don't go too fast...the good stuff is tougher to get than the coins and if you're hasty you'll go right over it. In the water, look for dips and troughs and pockets where stuff can settle.
That's about it...
