As with everything else, preparation makes demolition run smoothly. Before you get out the old sledge-hammer, make sure you've taken care of a few preliminary details:
Where's the old stuff going?
Can the cabinets be reused in the garage or basement? Or are they garbage?
Can the counter top be used in the garage or basement? Or sold? Or just thrown out?
Are the old appliances being keep? Can they be sold?
Do you need to rent a dumpster? Or two? Or more?
Have the sink and dishwasher unhooked.
Have gas ranges unhooked.
Even if you're not busting into a wall, it's a good idea to have the room's electricity off...just in case.
If you're doing the demolition with the help of a few friends, make sure everyone's working together. Several people randomly tearing stuff up makes for a huge mess.
In general, the order of demolition should go like this:
Water, electricity off
Unhook sink, dishwasher, and fridge (if it has water running to it)
Unhook gas range
Remove appliances
Remove counters
Remove cabinets
Remove flooring
Remove damaged sheetrock or plaster
With structural changes add:
Remove sheetrock or plaster where necessary
Remove framing where necessary
Try to keep the area as clean as possible. Sweep or use a shop vac every night. Don't leave debris laying around.
There's no turning back now. Your old kitchen is gone and it's not coming back.