Pick one outcome
Start with one observable change, such as getting the racket ready earlier or keeping contact in front. A single focus gives your attention somewhere specific to go when the pace increases.
Use a simple progression
Begin with slow, comfortable repetitions. Then add movement, a target, and more realistic pace one step at a time. If the change disappears, return to the last version you could repeat with control.
Check the change
At the end of the session, record a few repetitions from the same angle. A recheck is useful because it compares the new clip with the original focus instead of asking you to remember how it felt.
Improvement does not require every repetition to look perfect. Look for a clearer pattern and a next step you can repeat.