Leave the campground cleaner than you found it.
The retrospective meeting is the most obvious practice which works towards this goal. This check is enforced at least once every iteration, and is there to make sure you are in fact getting better and not stagnating or even starting to slip.
Some (otherwise) great agile teams seems to fall back into complacency and, dare I say it, laziness, after a while. This is like code entropy, but for the team. The result is that continuous improvement suffers and the team eventually falls back to a pre-agile state. Here are some indicators that the team is slipping into complacency:
- Retrospectives are becoming a boring routine
- Stand-up meetings no longer creates energy for the team
- Less pair programming and/or pairs rarely switches
- The whole team is getting more quiet
- Agreed-upon practices are skipped in silent agreement
- Workarounds are accepted instead of fearless problem solving
- Bugs are starting to appear again
You might consider using any of the online agile assessment tests or bring in experienced people from outside the team to help challenge the status quo.