Can't say in details. Broadly:

* checking specific configuration items,

* performing deployment in a specific order (even when it doesn't matter),

* testing deployment step-wise (so you know certain things work when debugging something that doesn't)

... and so on. We start with a checklist, and we then push as much as we can do automated scripts. At the end of a deployment we have a checklist to ask what can be moved from checklists to scripts. Next time round we do both to check that the script works, then reduce the checklist.

Lather, rinse, repeat.

It's making it "the norm" that's having the biggest effect. People are starting to know that certain things will work, and it releases them from tedious checking.