Once you know that your stroke is deadly straight, you can work on improving your pocketing skills with a few basic drills. Here's one that should challenge you. It's a progressive drill, which means that it gets progressively harder as you go along.
Set up an object ball near, but not frozen to, the bottom rail, at approximately one diamond from the corner pocket. Then set the cue ball along the same rail approximately one diamond from the opposite corner pocket and shoot the object ball into the pocket. Pretty easy, right? Just wait. Here comes the hard stuff.
Next, place the object ball in the same spot but this time place the cue ball farther off of the bottom rail, leaving a slight angle on the shot. After you pocket the object ball, set it up again and move the cue ball farther off of the rail. Repeat this movement of the cue ball after you pocket each shot.
But remember: If you miss, you must start the drill all over again!
Do you notice how the shots get tougher as you go along? That's the progressive part. When you can successfully pocket each ball without missing, you're on your way to becoming a cut-shot expert!
Practice your cut shots by setting up a drill like this one.