To add to my earlier point about self improvement.
Just remember that sometimes you need to allow yourself the freedom to not "be the best" and indeed, even to fail. Because sometimes focussing on "being the best" might not actually get you to your goal. Often you can end up trying too hard with these things, and as a result stymie your own creative juices. You over prepare, you get writer's block, or just stop taking risks because of the fear of failure. As a consequence, you don't enjoy yourself, and neither do your players. Of course, your drive to be the best demands a regime of rigid self criticism, which becomes either self indulgent or crippling...
Sometimes you need to allow yourself the freedom to not perform at your peak powers 100% of the time - to not be permanently "trying". Sometimes, to let creativity flow, you just need to just do the basics well. Keith Johnstone, the guru of improvisational performance, was renowned for yelling "be more obvious!!" at his students. He did it when they were trying too hard to be "original", because someone on the spot - striving too hard to be clever and original - can just freeze up, feeling that none of their ideas are adequate. Alternatively, they can come out with all sorts of clever-clever stupidities, which are only original because no one else in their right minds would normally put them in a scene...
One of his basic tools of creating a story was getting the people in a scene to simply "break the routine", i.e., take a simple story and change it, even in some small way, so that it is no longer so mundane. You can do this at every stage of the creative process.
An example: in classic chivalric stories the princess needs to be rescued from the dragon. This is now a routine that is well known to our audience, so lets "Break the Routine" 5 ways and see what it gives us:
1) The Princess is not captured by the dragon but loves the dragon,
2) The Dragon does not live in a cave, but on a cloud in the sky,
3) The Dragon was once a princess, and every hundred years passes on the curse to a new princess, who becomes the dragon while the original princess is freed,
4) The Dragon is on the endangered list, so the PC's are not allowed to hurt the dragon,
5) The princess is already dead. What do the PC's do now that they have failed in their commission...
I came up with these on the spot, breaking the routine in different ways
to see what appeals. On reflection, I would argue that number 1 has been done so much these days that it is a routine in of itself, and that number 2 is just a variant on Jack in the Beanstalk. I'd probably go with number 3 and see where it goes (which Princess do you rescue?) *
Do the basics well, add some simple twists, and focus on your players having a good time, and you will end up being a great GM.
*In fact, I like it so much I think I will run it!