Bottom english (backspin) is a valuable tool if not overused. It also happens to be a fundamental element in the game that should be mastered early. The best way to learn is through practice. Start by placing the cue ball 6 to 8 inches from the object ball. Shoot straight at the object ball, striking the cue ball one cue tip below center. Your stroke should be medium speed. Be sure to follow through, do not jerk the stick back, and stay down over the table. Do not elevate the butt of the stick. Don't worry about sinking the object ball. If the cue ball jumps up when you stroke, you either struck it too far below center, elevated the butt of the cue stick, jerked the cue stick back, shot too hard, or all of the above. Try it again. Keep on trying it. Pay attention to what the cue ball does, even if you fail. You can apply what you discover as well as what you learn.
Keep practicing the same shot until the cue ball draws back several inches. Now move the cue ball back further from the object ball (10 or 12 inches) and try again. After mastering one distance, move the cue ball back and master another. Keep in mind that shooting hard does not increase draw when you are relatively close to the object ball. To increase draw at a close distance, lower the point where the cue tip will strike the cue ball, but don't shoot harder. Shooting hard can cause the cue tip leather to loose friction with the cue ball, causing it to jump rather than spin. O.K. You say you have seen advanced players shoot hard with bottom english and draw the cue ball, even when it is a full table's length from the object ball? I don't advise this technique to beginners, but I will explain what the pros are doing. It is physics.
Since it is not possible to put enough backspin on the cue ball to overcome table friction for the length of the table, advanced players reduce table friction by causing the cue ball to elevate slightly. This reduces table friction and allows the backspin to hold until it reaches the object ball. They do elevate the butt of the stick slightly, which drives the cue ball into the table causing it to "jump" with backspin. It is a controlled violation of the rule against elevating the butt of the stick. Improperly executed, the cue ball will masse' resulting in a terrible miss and loss of game. It is a difficult technique, and I recommend against it. There are too many other options, such as hitting a rail first, or selecting another shot. However, it is a shot that applies the laws of physics, and that is what I think is important to remember.
There is a draw technique applied by advanced players. Many develop a certain "snap" to their shot by going from a relaxed to a firm grip at the moment of contact with cue ball. This technique causes the cue tip to "rake" downward on the cue ball adding to the backspin without having to hit it lower. It is an "acquired" technique that varies from player to player. In time you will develop it, but you won't know when. It is one of the more creative strokes that keeps us coming back for more.
Regardless of the techniques learned for various shots, the only way to master them is through proper practice. Don't cheat yourself by "banging the balls around" and calling it practice. Practice is work, and there is no alternative. Tour players spend long hours playing in tournaments, but they still practice regularly. If you think you know more than they do, challenge one to a game sometime.
If I can answer questions or defend myself against criticism, drop me a line.
Happy Shooting! Jim & Pat