Do you identify as a great public speaker? How you perceive yourself has a great impact in the way the audience will perceive you.
In my experience, those people who are good at speaking generally know that they are good and they act like it, going into every speaking opportunity with confidence. On the other hand, I have also seen people who were good speakers, but started to second guess and doubt themselves. Three fourth of the way into their speech, they are alright. However, if they make even a little mistake, they begin to get flustered and apologize. Do not do that!
I can say that I am the greatest golfer ever, but that will not help my golf skills to improve. Speaking, however, is different. You simply act like you are good. Yous still have to practice and give a good speech, but this extra element of believing that you are good will make both, practice and activities easier.
This is, however, no reason to skip out on or miss a practice session with your speech. In fact, it should only serve to motivate you to rehearse and practice more and become a great speaker in actuality.