Customer churn - how do you try to get them to stay?

I asked this on reddit, but asking here too!

I'm working on an internal tool to help reduce customer churn and would like some of your input.

I know the reasons for high churn rates might be highly specific to each individual business, but I'm hoping that getting general ideas and feedback from a whole range of people would give me a better idea of what exactly to do and to come up with more creative solutions.

The kinds of things I'd like input in is;

Do you have some sort of way to know which customers will like leave in the near future?

Do you have an automated or build-in system to assist you with retention? If so, what does it involve?

Do you offer discounts or added-value propositions to customers to keep them onboard? If so, what do you do? How do you prevent abuse? And if you don't offer discounts, what do you offer?

Do you do exit interviews with customers who have left? How and through which channels? What kind of questions do you ask?

What kink of data, metrics and statistics do you collect to combat churn? Or what data would you theorically like to collect but don't currently. How of do you keep an eye on this?

What is a acceptable churn rate even? Is there such a thing? Is it industry-specific? Where can I get data on this?

How do you relate and/or manage churn to other business functions, like perhaps having a mismatch between marketing and customar expectations?

If you have any other ideas or suggestion, please share!