You can set up and stroke across the table over the baulk line.
No Ball
You will be able see if your cue is running straight above the line or if the tip is moving around.
When you can do this smoothly, progress to shooting the cue ball along the baulk line and returning to your cue tip.
This is a far tougher exercise because it may introduce new problems:
Inability to identify the centre of the cue ball
Inability to hit the centre of the cue ball
Inability send the cue through the vertical axis of the ball.
Any of these problems will send the cue ball off on an angle on the rebound.
Snooker players call it "
hitting across the cue ball".
Solutions
Visual feedback before striking the cue ball:
Joe Tucker's Third Eye gizmo
A mirror set up at the end of the table.
A friend standing in front or behind you telling you if you are properly aligned.
Feeback
You can video yourself: back, front, and side; sometimes the only way to prove that the player isn't doing what he thinks he is doing.
When you have mastered the side to side return to the cue tip, you can progress to Bob Jewett's exercise down the centre of the table.
Be advised that the foregoing is only theory I have heard. Can't execute worth a damn


