Have a load of new saltwater at the ready - as much as half your volume if you can manage. Things can go nasty during moves, and you may need large water changes during or afterwards. Have lots of buckets and containers.
Drain the tank down into containers (half-full), put the rocks and corals into these. Then you can catch your fish a lot easier (save one bucket of tank water just for fish). As you drain down to the sandbed, you may not want to keep that last few inches of water - kind of sludgy. As long as the sandbed is wet, it will be fine for the move.
Get lots of friends to move the tank up the stairs...
