Just as having honest, personal communication. Being direct and not circling around the issue can greatly help any team.
Be direct, get to concrete examples and show them what you mean.
Be direct, but don't be an ass.
You can have direct, honest communication without being an ass. Be hard on the problem, easy on the person. rings true here as well.
Reference
Fried, Jason, and David Heinemeier Hansson. Rework. 1st ed, Crown Business, 2010.
Highlights or timestamps
One defining characteristic of a good environment is directness in communication. Avoid abstractions and long-winded, high-level explanations. Get real, and show your team exactly what you mean. Don’t sit in meeting rooms discussing problems but go to the problem sites themselves to get a grip on what’s wrong.
— ^acee1f from Rework