Although many people advocate that drills and practicing certain shots over and over again is the essential way to practice, I believe otherwise. Most people simply throw balls on the table and run out, which is naturally criticized. There have been several studies and books (unrelated to pool) that show when learning something new such as writing cursive you learn the best by practicing all elements of the skill at once. For example, you would practice writing all the letters of the alphabet in cursive at the same time instead of writing the same letter over and over. It's no doubt the slowest way to learn, but it also the best. In pool, when you shoot the same kind of shot over and over, you're consciously focusing on that one shot in that one scenario. You may become consciously better at that one shot quicker, but trying to combine the various shots from practice to a game in various scenarios will be overwhelming while throwing other parts of your game off. Let’s say you practice the exact same shot 200 times in a row. Then in a game situation, that shot finally comes up, but this time it’s at a slightly different angle and in order to get position to the next ball you have to use different English with a different stroke. You’re practice really wouldn’t of helped as much as you had hoped. If you instead practice like you’re playing the game, all of the elements of every shot would eventually become engraved subconsciously and those minor differences on every shot will have been practiced unknowingly at some point or another. There are too many variations on every shot to consciously practice all of them separately.
In my opinion, the best way to practice is to just throw balls on the table and run out as long as you don't start just banging balls like most people do. This way you're practicing all elements of the game at once without consciously focusing on any one particular shot too much, which will train your subconscious better. Pool is supposed to come natural from the subconscious when competing. You're not supposed to have to think.
In my personal experience I have rarely done any drills, and always practiced just by running out balls or playing the ghost even before knowing the best way to practice. I practiced that way because it was the most fun. When I did do drills or tried to practice the same shot over and over, it felt like I was focusing too much while becoming extremely bored. In the past two years my game has shot up tremendously without much conscious effort in the way I practice. Now, my game is completely unconscious, and I don't know how I make the balls or get shape; it just happens. I don’t consciously compensate for English, nor could I probably explain how to do so, but it happens somehow in my subconscious.
That’s just my personal opinion on the subject. Feel free to object!