Misses
Most misses come from just not paying attention enough to the shot, or trying to do too much with the shot for position on the next ball.
When I first started playing, I worked on making shots. Then after Jimmy Caras told me personally that controlling the cue ball was 70% of the game, I worked intensely on cue ball control by doing this:
I mentally divided the cue ball with 4 rows down and 3 columns. I practiced with each shot I shot using 12 different types of English, and watched the cue ball, where it went, speed control, etc.. Pretty soon, I was getting pretty good control for position play. Yes, I actually shot the same shot 12 times for each practice ball I shot.
I then went back to work on my aiming some more, being able to use different types of english on the shots, and learning how to throw the shot with english, spin shots, draw shots, stun shots, etc..
After that I worked on banking and knowing my rails. Safety play came in much later.