While waiting for their opponent to return from the bar or telephone many players practice potting the three baulk colours from their spots.
Here is something you may find more useful.
Place the cue-ball so it's touching the green, and try to hit the pack of reds. Play this stroke with plenty of bottom and right-hand side and aim as shown.
Studying the course the cue-ball takes from cushion to cushion will increase your knowledge of the angles, and give you reference points that will be of great use when you're faced with a similar position in actual play.
Vary this routine by placing the cue-ball behind the brown and yellow, and remember to stop the cue-ball to save re-racking the reds!