Well first of all heres 1 style of trap I use which is actually illsuited for the task due to the large size of the mesh
Theres also another type with a much finer mesh that catchs a great deal more. Basically they work like any crab trap with a raised entrance they can go in through but not escape.
Shrimp over here love structure especially weed bed's so I just go to the water mark and cast them in as close to the weed beds as possible. I use lamb as bait but potatoe is also know to be a good bait either way I get a good haul probally because no one else knows about this place.