The premise of sandbag fitness is simple. You practice the exercises, follow the workouts and record your performance. You consistently try to improve your technique in each of the exercises and, if necessary, try to move from a beginners version to the gold-standard or advanced version.
You should also record all of your perfromances in the workouts. Over time, you'll be looking to improve these. This could be a faster time for a set workout, progressing to a heavier sandbag, adding more repetitions or simply improving your technique.