Process improvement that sticks
Change one thing at a time and measure it. That's the whole game.
Pick one number
Callbacks per 100 jobs. Average ticket time. First-time-fix rate. Pick one. Improve it. Then pick the next.
Change one variable
When owners change five things at once and the number moves, they don't know which change did it. They can't repeat the win and they can't undo the loss.
Measure for at least a month
One good week or one bad week isn't signal. Four weeks starts to be.
Take your version of this question further
This is one operator-tested angle on the question. Your shop, your size, your trade, and your team change the answer. Ask your specific version inside Ask a Shop Owner to get a response grounded in how owners like you actually handled it.