I take mine off and blow the pistons out every couple of tires. I clean the pistons like
new with the same kind of brake fluid I'm putting back in and some of that 1500 grit
wet/dry sandpaper, and I clean the outsides of the calipers up with the wire brush
or whatever works...

I'm a big proponent of somehow cleaning the pistons before adding new brake shoes, else
you'll mash some of the old-nasty-previously-exposed piston back into the caliper when you
put on the new thick pads...
-Mike