How do you actually know if your business is doing well?

I’m trying to learn from people who are actually running businesses.
When you look at your business, what numbers do you personally pay attention to?
Revenue? Profit? Cash flow? Expenses? Something else?
And do you use software, Excel, an accountant, or do you mostly keep track of things yourself?
I’m not selling anything — I’m genuinely curious about how other young entrepreneurs handle the financial side of running a business.
Would love to hear how you guys do it.