As explained above is first of all be a good communicator but also have a good synergy between know-being (savoir-être), and know-how (savoir-faire):
The know-how consists of training and experience acquired during the life of an employee. This may be followed by internal training or courses like those offered by organizations like the FAFIEC the FITEC or CNAM (for France at least).
The know-how is an achievement.
As we see the experience is very important to mount skill trades on the test.
Similarly, in the know-how, technical capabilities are important. Such as having good skills in Visual Basic for a scripter under QuickTest Pro (I do not list any here because it will be tedious and unnecessary).
The know-being is composed of qualities such as rigor, flexibility and the ability to not miss any details. Remove ambiguities on a feature, provide all the potential risks (or most), record each decision and verify the correct account.
Other qualities are to identify all the tasks without forgetting one, identify all the issues still pending and does not leave unanswered and keep track of each decision.
All this is different from the stiffness or inability to accept change his mind to adapt to a new situation, a new context, a new customer, etc.
It must be good communicator and know these ideas to express orally and in writing and listening skills: being open to dialogue. Either try to understand others (written and oral), have a certain openness to their ideas.
It must also be convincing (≠ « having a bad character »), and take into account the positions of the hierarchy or the customer entity (“maitrise d’ouvrage” in French) that are sometimes at odds with optimal conditions for the success of the project. It is important to hear his word and to convince his interlocutors with concrete and factual arguments.
Above all we must build its credibility with other actors (customer in first, developer, etc.). This may take weeks or even months to build the credibility but a few minutes to destroy it. It means be as factual as possible in the documents, committees and other relationships with other actors.