I'll give you what I did, although i suppose it depends on the size of your tank and its inhabitants. Mine was a 50ish litre tank with 4 oranda.
First of all, get three buckets.
Fill one with all plants, decorations etc.
Second one, fill half to 3/4's full, depending on how big the bucket is and how much you can carry, eg my cukets are 25 litres and i can only properly carry them when half full, but my old buckets were ten litres and i could easily carry them when full. Then add heater and filter, place in a quiet place and cover with a towel or lid. Add a couple of plants if you have skittish fish that like to hide.
Third one, use to siphon out the rest of the water including cleaning the gravel.
If you have gravel, consider taking half of it out and giving a good shower, to try and eliminate all that gunk. If you have sand you dont need to do this as long as you have cleaned it properly of all surface detritus.
Leave about an inch of water in the bottom to keep the sand/gravel wet.
Take everything to new house and plug in the heater and filter again at the new house. Keep the lid.towel on at all times and try and keep it dark as possible where the fish are.
Fill new tank and re-plant and put ornaments back in.
Test new water in the tank and water int he bucket.
If its different, acclimatise (if very different, acclimatise by drip, otherwise just the usual add water to bucket etc), if its exactly the same, take filter and heater out and put in the new tank, and add the fish.
Remember never to leave the heater out of water unless it has been turned off for at least 30mins, and leave lights off for at least 4 hours to help lower stress levels.
Dont feed for 24-48 hours.
Keep an eye on water stats (shouldnt be a problem if your filter was kept running)
Just a thought though, why do want to keep all the old water? Its a hassle and theres no beneficial bacteria in it contrary to popular belief!