Have more options when you don't have a direct shot.
The object ball hits the top rail and comes back to the side pocket. Treat the rail as a mirror: at medium speed the angle in is close to the angle out.
Video lesson
Key points
With no english and medium speed, the angle coming off the rail is close to the angle going in.
Hitting harder shortens the angle off the rail; running english lengthens it.
Use the diamonds on the rails (a diamond system) to estimate the path.
Common mistakes
Banking too hard, so the ball comes off short
Not paying attention to where the object ball will hit the rail
Drill
Put a ball in the middle of the table and bank it cross-side into the opposite side pocket: 10 shots at soft speed, 10 at medium speed. Compare where they land.