Of course, we all know that the most obvious component is hitting your routine, meaning each skill is completed smoothly and without falling.
Unfortunately, it's not enough to "just do a clean routine" if you want to get 9.00's or above from the judges. What the judges are looking for in a 9+ routine is a special spark. Every move, even those little insignificant gestures on beam, needs to be sharp and show that you're confident.
I saw many routines where the gymnasts simply went through the motions of their routine, without that "spark" aforementioned. Often, people underestimate the essential component of having an attitude that tells the judge, "Look at me! I'm confident at what I'm doing, and I'm having fun!" Now, while that may sound cocky or stuck-up, it's what the judges are looking for in a nine-worthy routine.
What does a confident routine look like? Especially on beam and floor for the girls, it means having sharp and sure movements, a smile on your face, keeping your chin up, straight legs, and extension all the way through your fingers and toes. If all these components are present at the same time, it will leave a positive impression on the judges. (Even if you didn't do as well as you would have liked, keeping a good attitude throughout and after your routine may save you a couple tenths.)
And this confidence comes from many repetitions in practice. When you've practiced well and to your full potential, you know that's the best of what you're capable of, and that should give you reason to be confident. Of course, we can't be sure of everything we do all the time, so once in a while you may have a new skill you haven't quite mastered, or one that's been giving you trouble. But even so, you shouldn't let that take away from confidence from the rest of the routine.
So, if you've been hitting your routines, but are wondering why your scores are only in the mid-eight range, have someone carefully evaluate your routine, or even better yet, have someone videotape your routine, and see what you can do add a little "sparkle" to it.
Remember, have fun, and good luck!