In Fortune magazine, Vicki Elmer has a good column on the growth in the use of executive coaches. She offers "four ways to make your coaching experience a success."
1. Find the right match.
2. Get clarity on your firm's expectations regarding the coach.
3. Come prepared with key issues to discuss when meeting with your coach.
4. Make sure the coach observes you interacting with peers and direct reports.
I would add that you shouldn't recommend that someone get a coach unless you think they are prepared/ready for that experience. Some people may need some other types of developmental experiences to establish a "readiness" to be coached. If you rush someone into a coaching relationship, they may not be willing yet to share their concerns about problems they are experiencing, or they may not even yet be fully aware of their areas requiring improvement. If that's the case, then they won't get the most of a coaching experience.