Separate the ones you are going to butcher and hold them in a pen or crate for at least 12 hours, preferably longer, with water but no food. You want their guts to be as empty as possible. I think it works best to take away their food in the morning of the day before slaughter, then that night take their water away as well so they don't drink in the morning - this keeps their crops empty and makes it much easier to pull out.
Slaughter as early in the morning as you possibly can manage, before first light if possible, the chickens will be torpid if it is still dark and they won't get so excited. Alternatively you can do it in the evening after they bed down, but this makes for a long day and increases the chances of messing things up.
Have a plan for all the bits: blood (catch in a bucket), guts (ditto), feathers (bag or bucket), meat (ice water or iced brine in a cooler). I like to have several large pieces of freezer paper cut in advance to put the meat on so it doesn't pick up gunk from the table.
Decide in advance if you want whole birds for roasting, or cut-up for frying etc. If you are going to cut them up anyway, I think it is much easier to do that before evisceration. Pluck, cut off the feet, then cut the thigh/leg assembly away from the body, then use poultry shears to cut the breast away from the back. Now the liver, heart, and gizzard are easily pulled out and cut away from the rest of the viscera; once you have done that, it's easy to dump the guts into a bucket, then pull the lungs/trachea/crop out and drop into the bucket.
Feet are worth the effort for the extra richness they bring to stock. I've found that they skin easier if scalded at a little higher temperature than you use for plucking, maybe 5 to 10 degrees hotter. Peel the yellow skin off and pull off the toenails.
Oh, and speaking of scalding - have a hose with a spray nozzle ready so you can wash off the bird after killing and before scalding. Otherwise your scalding water quickly becomes disgusting.
I like to chill the meat in an iced brine instead of plain ice water; the brine draws moisture out of the meat so it doesn't get waterlogged. About 1/2 cup salt per gallon of water is plenty. Leave meat in brine for 2 to 8 hours, then rinse off and let air-dry in the fridge, or in a cooler with some blue ice or bagged ice, for 24 to 48 hours before packaging.
