Experience:
- working in strictly timeboxed iterations with adaptive planning using some sort of prioritized work list
- working in a "test-driven" manner (e.g. writing a document for a client where the client specifies acceptance criteria)
- participating in frequent status meetings where the team members report to each other, commit to work and identify barriers
- building and maintaining big visible charts to show progress and status (e.g. the standard thermometer chart to show progress towards a numerical goal)
- fashioning appropriate tracking and performance metrics that encourage team work rather than individual competition
- helping other people to adopt and adapt all these practices

Capabilities:
- promoting collaboration in challenging circumstances
- searching for truth/a solution relentlessly
- honesty and trustworthiness
- a learning attitude (proactive and learning from mistakes)
- humility and assertiveness
- guiding people without controlling them
- detachment (ability to step out of a situation)
- an attitude of service without expecting recompense
- understanding of transformative learning
- conflict resolution as learning (not negotiation)
- encouraging creativity

Not Required:- technical experience related to the work of the team - the Agile Coach (process facilitator) should not be a performer on the team
- domain experience related to the goal of the work - the Agile Coach should not be a direct stakeholder in the results of the work

However, technical experience and domain experience can sometimes help...

Suggestions and ideas are greatly appreciated!