Public speaking is like any other skill in life, you're either making it better or worse, it's very unlikely you're going to stay at the exact same level. My advice for you would be, have specific goals for yourself. have specific improvement plans if you're used to speaking in front of 50 people, but once a year, you could speak at your national trade show or your national sales convention in front of 500 people and you're a little bit scared. Start doing the things now to prepare you to speak in that venue. Always look for something that's the next level up. Doesn't matter where you are.
In the speaking world. There's always something that is a notch or two above. So start planning now start preparing, hold yourself accountable. Doesn't matter how long you've been doing this you need to record every speech you give and watch it so you can figure out what are you doing well, so you can do it more. Sometimes it's one tiny little thing But over time, it is huge. It's quite significant to make small, tiny, incremental improvements.
Also, you need to create a database of speakers you admire and respect so you can learn from them. These days with Apple TV, Internet TV, I find it's frankly more relaxing and more interesting to just flip on TED Talks, and watch great speakers than it is some lame sitcom for entertainment. I always learned something, even if it's a speaker, I'm not fascinated by the subject matter. You can always learn something about their style, their technique, their visuals, their interaction, their movement, so if you want to be a great speaker, it has to become a life long passion.