I was talking to a great person at a firm that will not be named.
He is in charge of a large implementation of agile for a large group within a much larger organization.
They start their teams with agile (Scrum) training and a hands-on workshop. And also provide coaching to each team from a senior agile coach. It is hard (in simple terms, due to overcoming the company culture), but they are making progress.
He said after 18-24 months into the transition, he has two big lessons (for himself).
1. Must have full-time ScrumMasters. And develop them.
2. Must have better Product Owners (and full-time). Specifically, for one thing, must have them take the Product Owner course.
Lots of other things to fix and improve (as is always the case). But those were the two biggest lessons.
One of his big lessons for the product owners is what I will say this way:
"Never do the 100%-100% rule ever again!"
This is a play on Pareto's 80-20 rule. And what he is driving toward is very similar to the Minimum Marketable Feature Set idea (discussed, for example, in "Software By Numbers" by Mark Denne). He is not sure they will ever succeed in doing the 80-20 rule, but for sure they can stop doing the 100-100 rule.
A few key, actionable ideas, not from me, but from someone in the trenches. Perhaps they are helpful to you.