Everybody does things a little bit different. However, there are a few things to understand that might help you figure out what will work best for you. I'm sure I won't capture everything here but perhaps it will help and maybe others can contribute too.
1. Many times you will need to partially drain the tank to get the lifestock out. Keep as much tank water as possible and try to siphon as much off as possible before disturbing items in the tank.
2. Liverock WILL have detritus in it and when that is disturbed (by you moving it around), it can and will foul the water it is in. Depending on how concentrated that water is, you may not want to use it in the end.
3. As mentioned, sand is a throw-away. It's cheap to buy and a bear to try and clean. Just replace it. $50 now beats losing livestock after you've changed the tank.
4. Everything will get stressed, adding to the mess in the water.
That being said, I've swapped tanks and moved across country with virtually no losses a couple of times by doing this...
1. Buy & pre-rinse all your sand ahead of time. Store in fresh salt water in closed 5 gallon buckets.
2. pre-mix and pre-heat as much water as you can. You WILL use it.
3. capture as much tank water as you can and reuse it as it is a known stable environment.
4. store your livestock in a cooler or tub with heat, aeration and some flow. They can survive without light and be in this environment for up to a week without loss.
5. Liverock kept in temp-controlled water will be fine for 1-2 days but expect it to start dying off & stinking after that.
6. Keep the corals separate from the livestock wherever possible and don't reuse the water from it.
Personally, I kept my fish & corals in separate containers that were 70% new mix water, 30% tank water. I bottled up tank water and reused it, ultimately using about 50% of the "old" tank water in the new setup.
Add your sand, do your aquascaping, and let that come to temp and settle before putting any fish/corals back in.
PLAN PLAN PLAN... You can't plan enough to do this. Avoid doing it over hoilday weekends or times when home depot/etc or LFS are closed. Extra buckets, towels & MONEY will always be necessary.
A tank move will take at LEAST one full day if not 2-4. Many people underestimate the amount of time it takes to move a tank. They fail to account for time to plumb, wire, level, etc etc etc, and when they fail to account for the time, their livestock starts dying because they weren't prepared to deal with it.
