What are your key takeaways/must-do's when implementing a CS software?

Hi all!

I have implemented 2 CS tools in the past few years, but I am still looking for a 'best' way to actually go about it. Learned some practical elements about software implementation, but I am looking at finding ideas/plans on the 'what' and 'how'. I have yet to come across good implementation plans, so would love to hear your thoughts!

To those who have implemented CS tool in your teams:

1. Where did you start?
2. What is a must-have or must-do for you?
3. What prep work did you do, before kicking off? (big learning for me: lots of prep to have in place)
4. What data did you have available?
5. What processes were well-defined before starting?
6. Where did you fail?
7. Anything else you can share...?

Thank you in advance!