If you are hitting balls by yourself, you want to make sure you don't get sloppy with your routine. Drills force you to concentrate and are excellent for practice, but sometimes they are not as enjoyable as just running a rack.
Try this exercise that feels like playing a game of 9-ball. Start by putting the 1-9 balls randomly on the table, but do not create any clusters. Take ball in hand to put the cue ball anywhere you want, then start your run in order, just like 9-ball.
If you make a mistake, either by missing the shot or poor positioning, then reposition the balls to shoot the previous shot again. The placement does not have to be perfect, but close enough where you would consider it the same type of shot. Keep shooting the shot until you are able to continue your run.
Eventually, you will have ran the entire rack, just not always on the first attempt. You will get to practice the shots you missed, and you will feel good that you are capable of running a rack like that!