Briefings generally include (although there are no DMs on UK boats, and briefing is given by the skipper, they are the same):
Before leaving the dock:
Length of the journey to the wreck
Boat safety and emergency procedures
First aid, O2, life raft, fire extinguisher location
How to get on and off the boat if there are any new to the boat customers
Filling out the log sheet with expected dive times, emergency contact info, and gas mix
If it's a shuttle and not a charter the "Please don't make your run time longer than X as we have to get back for the next run. So those of you planning on more than 15-20 minutes of deco, please re-plan your dives" speech.
And handing out of tea/coffee/hot chocolate followed by banter
At the dive site
Approximately where the shot has been dropped, and it's relation to certain features on the wreck. Current depth, which shouldn't be a surprise as people know what they booked onto
How to ascend, either coming back up the shot (rare) or putting up a DSMB (most common)
Re-iterate max run time allowed if applicable
Re-iterate how to get off the boat and exiting procedures
Re-iterate how to get back on the boat, where to go once you surface and the boat begins to head towards you, and any other site specific exiting procedures (there is one area where I dive quite often, inside a harbour. More often than not, as most of the wrecks aren't too far from the harbour wall, we need to swim away from the wall before the boat can safely pick us up).