Study Endgame Positions

Learning a lot from Paul Keres' masterpiece "Practical Chess Endings" is a must although there are better books now. With good reason he quoted something like "for someone to beat me they have to beat me in the opening, the middlegame and the endgame" and "A player can sometimes afford the luxury of an inaccurate move, or even a definite error, in the opening or middlegame without necessarily obtaining a lost position. In the endgame an error can be decisive, and we are rarely presented with a second chance". You may re-read through that book and engrain the patterns again in your mind, because in the beginning you would easily forget. How exactly do you win with Q+K vs R+K again?