a basic principle, rule, law, or the like, that serves as the groundwork of a system; essential part: to master the fundamentals of a trade.
In the "trade" of pocket billiards, there are a number of essential parts, each of which includes basic principles. When put together you have the groundwork of the system of playing more effectively.
You must have a shooting platform from which your battles against the world are launched. This starts with the placement of your feet. Your entire body mass must be well distributed and balanced. Without that stability, any movement elsewhere in your body will move something else, forcing you off balance.
As you bend over your stick, it needs to rest lightly upon your bridge hand. This means that your stick hand should be gripping the cue stick just in back of the balance point. The cue stick should also be as close to parallel to the table bed as possible.
As the stick moves forward and backward, propelled by your stick arm, the cue tip should be a true back and forth movement with no wobbling side to side. The shaft should not drag on the fingers of your bridge hand. Below your elbow is where the only major action of your body should take place on a stroke. Up to the contact of the tip on the ball, only the forearm moves. Any other body movement is detrimental to the stroke.
Your head and eyes must be aligned above the cue so that the aiming line can be imagined properly. There are thousands of words written about dominant eye alignment, chin height, and so on. It is enough to know that the head position is the visual input that your brain needs to calculate the aiming line that the cue ball will travel. If it is off to one side that skews your viewpoint which provides wrong information to the brain.
The stroke is the physical action taken to get the cue ball moving on the table. All ball movement that occurs on the table can only occur with the single, very momentary contact between the cue tip of your stick and the cue ball.
The key to successful stroking is the precise placement of the tip on the cue ball and the speed of the contact, followed by the follow-through. From that contact, the cue ball travels down the table, contacts the object ball. Whatever laws of physics that you applied will determine how the cue ball acts until it finally comes to rest. Everything else is the consequences of that action.
The brain is used in two ways. One part contains the automated activities necessary to accomplish a shot. Among these are the necessary body positions for every type of shot that have been learned from countless thousands of repetitive efforts. (This is why it is so hard to learn a new body position change - it has to constantly fight the established habits. Only when you have forced the new change over the top of those by another set of thousands of efforts can you successfully make the change.)
The second part contains the history of every shot you have ever taken along with its success or failure. This is your Shot Library. When calculating the different ways of shooting the shot, you are actually sorting through every similar shot you have ever made. Your library is trying to find the closest set of related patterns to the current situation. When you have a situation with no previous experience, you have to cut and paste other experiences into something that is worth a try. Upon execution, that shot and its results become a part of your history.
Stance, Stroke, and Brain are the three fundamental basics of your game. When these are integrated together into a functioning operation, you have the basis to become the shooter you deserve to be. To further improve your skills, focus on smaller and smaller pieces of these basics.
For example, to improve your draw, focus on a smooth stroke aimed at a precise point on the cue ball. When you can execute the shot consistently, you can have trustworthy results. With positive feedback from practices, you learn how to draw the cue ball back to per-determined positions.
Improve any of these fundamentals by working out what needs to be changed and then practicing that improvement until you own it. Bit by bit, you can get better every day.