Lose the fancy stuff -- no spinning crescent kick sort of nonsense. Make your body fit and strong and make each move economical and count.
If you get something like a heavy bag just don't beat it up like a maniac. You're supposed to imagine fighting someone. When bag swings to you, you focus on footwork, dodge, counter. Then when the bag swings away, you drive your power into it and then have discipline to put o the brakes as it swings back.
All balance, rhythm, timing. People have their weaknesses and it is not in the body but in their balance. You can't learn this on your own that well but it helps to just be aware of it.
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It should also be noted that even if you go to a class, you might not actually learn all that much useful :D Avoid the mcdojos. Sparring is important. Even some basic level sparring. You don't have to kill each other, but there needs to be some resistance and idea how to deal with basic things.
Thank you so much for this!!