Ok; it depends a bit on how far you're moving as to how much water you want to save; the further away you're going, the more likely it is the water will be different, and you'll want to take more of your old water, but the basic method is this;
Switch off your electrics, and remove them from the tank, not forgetting to let your heater cool down first, and, depending on what kind of filters you have either put the media into a fish bag with a small amount of water, or put the whole filter in a fish bag or bucket; you don't want it to dry out, it must be kept damp.
Syphon off clean water from the top of your tank into your containers; the more the better.
Then take all your plants and decor out; wrap the plants in damp newspaper. Take more water out, leaving just enough for the fish to swim upright; this makes catching them a lot easier!
Catch your fish and bag them up, if you can (most LFS will give/sell you some fish bags) or put them in a
covered bucket. You want one third water, two thirds air in their containers.
Empty the tank of
everything, including substrate; tanks are not made to cope with the stresses of being moved with anything in them. The water that's left will probably be pretty murky, so get rid of that.
Move everything to your new place.
Set the tank up, add the substrate, plants and decor and then your saved water. Put your electrics back in, switch the heater on, and the filter, if you have enough depth of water to do that.
Float your fish, as if they were new, and release them.
Top up the tank with new water, just as you would for a normal water change; done!
As long as you don't let your filter media dry out and you don't dump the fish into loads of new water, you shouldn't lose any
