The main thing you need to have is the GPS coordinates of the marine sanctuary areas.
http://floridakeys.noaa.gov/tortugas/currentplans/implementation.html
Aside from those, the best sites we ran into were in the 40-60 ft range.
If you dare, watch the currents, drop in near the sanc zones, and drift away from em. We did this on the southernmost border of the sanc zone on the NW quadrant, southern end of the Tortugas bank. On a typical gin clear water day in the DTs you can see bottom and spot the reef areas. Aside from that, try spotting lobster buoys. Look but do not poach the traps.
The other area we usually had decent luck in is the Marquesas bank and Rebecca Shoals, although you'll need a depth sounder to find the mounds in 70-80 ft of milky 30 ft vis,
orrrrrrr head for the shallows during low tide and fly between the rocks on the shifting tide.
When I say fly, I mean fly! The current gets moving thru the shallows so you basically fin from rock to next rock down-current, check for bugs, catch em, next rock ...
Sorry, no GPS coords, but my two cents worth from a handful of lobster trips.
Good luck!