It's the first 'job' I learned how to do, quite easy.

Front or rear brakes? Fronts do not need shims. Rear OEM pads come with builtin shims.

Stop at a local parts store and buy a small tube of silicone brake grease. One small packet will be enough to do several brake jobs.

Use the brake grease on the rubber piston boot and the slide pin (which you cleaned and removed all of the black dirt).

Rotors? There is a minimum thickness which I usually ignore. I replace the front rotor every other pad change. Older rotors will show a 'lip' at the outer edge, and when that gets thick (actually the pad rubbing the surface makes the rotor thinner by that much), replace it. Yes, the rotor can be 'turned' once, but a shop has to do that.

Using brake cleaner on the pad surface helps the pads break-in, and cleaning the rotors gets your nasty finger prints off.
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My back feels better when I sit in a Volvo seat