Is it front's your doing, the AD22VF's? I've done about 6 sets of these over the years...
First of all, clean the outside of the caliper with a wire brush to remove all the brake dust and dirt.
Pop the piston out of the caliper - i use a foot pump with a tapered nozzle fitting and some bluetack to create a seal between the taper and the fluid inlet port. Best to put a block of wood inside the claws of the caliper to stop the piston shooting out and becoming damaged as they're plated.
Once the piston is out, rip the piston outer dust boot out and remove the circlip that held it in if it didn't come out with the boot. It's just a metal ring if i remember right, and all you need is a screwdriver. You really need to clean this area up along with the very top inner edge of the caliper bore as this is where rust forms and binds the piston.
Once you've done this you'll see the inner seal sitting near the top of the bore, carefully remove this with some kind of fine pick.
Once all cleaned it should look like the pic below. Note that i wash the stripped calipers in the sink for a final clean to get all the rust and gunk out. With water contact like this though, it's imperative to immediately dry inside with kitchen towel and wipe clean brake fluid across the inside surfaces, fluid port and bleed nipple port before flash rust sets in :
I've only ever cleaned the pistons and the bores with clean brake fluid, kitchen towel and an old toothbrush as you don't want to scratch the plating on the pistons. Brake fluid will remove all but the most stubborn residues around the top of the piston.
When cleaning the bores on the torque member for the guide/slide pins, if i remember right it's an 8mm drill bit that can be turned through them to remove the rust.
On the rebuild, you've got me. It's been a while and i have a hunch that i might have found it easier to fit the top of the outer piston dust boot to the piston itself, and then push the piston in a little and secure the bottom of the dust boot to the caliper. Someone else will have to chip in here as it's been a couple of years since i did my last set. I do remember though that you need to be damn careful not to puncture that outer dust boot when you put the securing ring in, both with the ring itself and the screwdriver or pick that you use.
Also, make sure you lube the piston seal inside the bore. I can't remember if that's supposed to be the red grease....
And if you're talking about rear calipers...not fun (apologies for crappy pic quality):