The shot diagrammed by I Rack Balls is the classic two-railer for this type of situation, and you must develop the ability to accurately send the cue ball to each of the diamonds on the third rail. In fact, that particular angle, on all object balls laying on the line between the one's position and the pocket is considered the ideal angle for moving the ball around two rails to the center of the table or at a specific point on the third rail. Set up shots of that nature and learn to do this using both the clock system and the vertical axis of the cue ball. I stress learning both ways because there will be times when you have to make this play with an elevated cue, and we know what english would do in that situation!
If you come out of this thread with nothing else though, remember these three things: 1. The key to successfully playing position is to consistently use natural routes that end up, as much as possible, bringing the cue ball down the line of the intended angle instead of going across it. 2. When you use the rails for shape, give yourself a specific target to hit. 3. 9-ball is a game of angles and patterns. There are certain patterns and types of shots for moving the ball across and up and down table that recur again and again. Get instructional material and watch top players to learn these patterns, and then put in the work to master them and make them your own.
Good luck, and remember to try without trying!