First thing is to check with your local and State agencues to see what the restrictions are. Wetlands, tidal or not, have a significant amount of regulation associated with them so make sure you meet the code.
I've put in a couple of piers and found it to be fairly straight foward. You have a couple of options. Floating or fixed.
Floating piers are supported by float drums or solid styrafoam blocks. These are readily available through any boating supply chain such as West marine or Boat US etc. Floating piers have the added advantage of being removable (if small) if you live in an area where you experience freezing. In addition, floating piers have the advantage in construciotn. You basically lay out the size, position the floats and build the deck on them. After completion you slide them in the water and anchor them. Any of the companies that provide the floats will provide all hardware and planning kits.
A fixed pier requires that you drive pilings which, of course, requires special equpment. I've seen folks put in pilings hydraulically, basically a trash pump is used to excavate the hole while the piling is being inserted. Works fairly well if you have a soft bottom. As there is no particlar support pad, except dirt/mud, a fixed piling needs to be driven fairly deeply.