A Tip that has not been mentioned is to open the bleeder when pushing the pistons back in. This gets rid of the old fluid/crap in the calipers [ where it accumulates] instead of sending it back up the line . Very important . This also makes piston much easier to push back in as there is no line pressure on the pistons. It also does not effect the masters res. level.
If doing pads on an ABS system, this is real important, as you can push the crap right back into the ABS unit ..big $$$ mistake.