Here is one of my endgames where I had a Rook and Pawn vs Rook.  It should have drawn, but my opponent misplayed the endgame.

3...Kd7  How is Kc8 a draw?

After 1...Kc6 2.Rd6+ Kxd6 3.Kxb6 Kd7 4.a4?? (4.Kb7 is the only way to win) 4...Kc8! 5.a5  Kb8 6.a6 Ka8 and any move for White is a draw.  7.a7, for example is a stalemate.

The trick I use for this is making sure my king can get to c8 -- if you can keep it out of c8 you win, as in this game.