It’s not difficult, but there are a lot of little details that get skipped quite often, mostly cleaning/rust removal. You technically should resurface or replace the rotors every time you change pads because it helps break in the pads. You should clean the hubs and rotor surfaces where the wheel mounts because debris /rust remaining can make the rotor /wheel not true. The calipers and brackets should also be cleaned and shims/other hardware should be replaced. Caliper bolts /slides should be cleaned / inspected / replaced. If there’s a torn boot on the caliper, then it should be replaced or rebuilt. If you don’t take the time to do it properly then there’s a good chance that the pads will wear out prematurely on one side or could seize up shortly after you do the brakes (happened to me one time) you should also flush the fluid if it looks very dirty as brake fluid is hygroscopic. It absorbs moisture which lowers its boiling point. If your brake fluid boils then your brakes won’t work.