Be conscious that being an agile coach does not require anything except claiming the title. Look for candidates that have a great growth mindset and adopt an open and flexible coaching stance.
A good agile coach will work with the leadership of an organisation to map out a transformation roadmap for a department, division or team. This roadmap will display structured skills growth cycles that can be monitored and assessed.
Coaches should always engage with their client teams with intent. The intent to learn, share and grow together. Coaches need to constantly review and prioritise their engagement messages so that they are consistent and clear with their client teams.
Many coaches distract and confuse their client teams by using new and flashy techniques to impress the team. This confused teams who are not yet confident in the basic nature of agile and lean practices. Coaches should introduce new techniques with caution.
Learn the rules, break the rules (with knowledge and observation), make the rules. This is very basic practice for a top of the line coach. Establish standard patterns of behaviours until they are habitual (Shu). Examine the effectiveness of the behaviours and work with the team to identify other ways of working and experiment with an eye on the outcome, looking for increased effectiveness (Ha). Re-establish baselines and norms based on the results of the experiments (Ri). This then cycles around as the "new" rules become the Shu.
Coaches can have a tendency to try to be the smartest person in the room, a coach should recognise the amazing contribution of all team members, adopt a humble and learning posture and look to integrate their knowledge into the team's knowledge - aiming to enable the team to coach themselves eventually. No coach should become a single point of failure for the team.