The common starting place for people with regards to draw, is are you hitting it low enough or hard enough or followthrough stroke... But that overlooks the true starting place that is the sole determinant of draw, which is actually "the SPIN of the cue ball" in the reverse direction at the point of contact with the object ball.
The other comments can be helpful factors in getting draw, but draw can be achieved without any 1 or more of those elements (low, hard, followthrough...) mentioned above. But, if you don't achieve the proper spin at the point of contact, then you'll never get draw. The benefit of this knowledge is that it puts focus on the true element for successful draw, instead of factors that are not as useful.
This raises another issue, which is be very careful of the instruction you receive regarding draw, because there are a number of different ways to achieve draw. One person may achieve draw one way, while another does it a quite different and even opposite way, so you could receive some very confusing or conflicting explanations. For example, 1 person could say that it's all about a long fluid follow through, while another person could say that a short snappy nip on the bottom but hard enough to reach the cue ball without losing the spin, would produce better results.
Since my focus is more on spin, then I'd actually say that it's ultimately about the amount of acceleration exerted on the cue ball at the right point. Getting physical for a moment, this acceleration would be the force needed to apply the proper angular rotation on the cue ball. In other words, "SPIN".
Therefore, one of the first things you want to do to achieve draw is to have some way of demonstrating whether you have the correct spin or not. Thus, when practicing draw, I'd recommend that you eliminate whitey and replace with either a striped ball (especially if you align the stripe, perpendicular to the line of draw desired) or measle dot cue ball. This factor alone will help you in two ways. 1. Being able to see the spin on the ball. And 2. the cue'd ball will definitely not be the heavy cue balls that are often required on some tables. Heavier cue balls will make it more difficult to draw. This is definitely not good when first learning.
Maybe try draw with the different cue'd ball 2-5 times to actually see what kind of spin you're putting on the ball, and to see the outcome (successful draw or not). At this point, it'd be wise to have someone who is comfortable with draw, execute the shot with the same cue'd ball. Now, you'll actually be able to see the difference between the spin you put on the ball which doesn't draw, and the spin your selected expert puts on the ball which does draw. This alone will give you a visual goal to head towards, and strive to achieve, which will head you towards a path of achieving the desired spin at the point of contact.
Identifying the problem result:
1. not generating spin
2. not generating the right kind of spin in the right direction (spinning left or right would significantly reduce effectiveness)
3. not generating enough spin to overcome the cancelling effects naturally caused by the friction between the cue ball and the felt as it travels towards the object ball
Once you identify the problem result, then people can more accurately relay the solution, if still necessary. With the information above you may already be able to achieve successful draw.
