ClearPM

"Project management is about accepting responsibility and exercising authority to get the project done. The role of the project manager transcends the traditional distinctions regarding job levels, seniority and organizational hierarchy. It is a leadership role that expects the project manager to acquire, direct and motivate the organizational resources to cooperate and perform in the context of the project."

Dhanu Kothari

My employer didn't hire me to tell a bunch of technical experts what to do.  Over the years I've worked in numerous areas of IT, but I think most of us will agree that since I haven't continued to work in those areas and I haven't focused on maintaning currency in a particular specialty, then I've probably lost that technical ability.  I've maintained an understanding because the foundational basics mostly remain the same and I get exposure to those areas in most of my projects, but the technological and implementation details fall away or become obsolete and unusable.

So if it's not my job to tell my team members what to do, what is my job?

Project managers make sure the work gets done.  As Mr. Kothari suggests, it's about leading a team to accomplish a goal.  In many organizations, the project team members don't report directly to the project manager.  The PM doesn't write their annual performance appraisals (though the PM probably does have some input).  But even if the team does report to the PM, you can't just rely on your explicit authority to get the most out of your team. 

• Personal relationships are the most effective way to motivate people to accomplish their work.  Given a choice, most people would prefer to make someone happy rather than disappoint them.  Of course it's not always that easy.  People have competing demands on their professional time and have to prioritize.  If they don't know the person asking them to do something, they're less likely to make the time to get it done.  A personal introduction goes a long way toward raising the priority on the work you ask that person to do.
• I wrote about this in another post, but personality assessments help you understand why your team members work the way they do.  Maybe you have two team members who just can't get along or work together.  What is the cause of that?  It's easy enough to say they just don't get along but not so easy to work around that roadblock.  A personality assessment might show that both have "directive" personalities, which might have already been obvious to you, but the assessment might also reveal other areas where they're more compatible.
• People generally want to do a good job.  People generally want to excel in their chosen career.  Rely on their professional integrity.  I've found that I don't need to continually harass my team members to get the work done.  I give them the task, tell them when I need it done, and get out of their way.  In most cases I can rely on them to get it done.  They're the experts, not me.  I'm not going to stand there and tell them how to do their jobs.  I follow up to make sure they aren't encountering any problems.  I get status information from them so I can report to my other stakeholders and make sure this task, timeline, and cost still fits in with my other project tasks, timelines, and costs.  But I rely on them to meet their professional obligations.
• Team communication is the bedrock of project management.  Without it, nothing gets done.  Telephone, e-mail, and even video communications are fine, but to build that personal relationship I mentioned earlier, face-to-face meetings are best.  Meet your team members as early in the project as possible.  This applies to projects and companies of all sizes, permanent or contract or consulting PM positions, and even if you already know one or more of your team members.  Continue to meet and communicate with your team members as often as necessary and sometimes even when it's not necessary. 
• Teams work best when everyone has goals that are being met as a result of being on the team.  This goes back to understanding your team members.  If you know some of their goals, personally or professionally, you can try to align their tasks with those goals.  You can discuss with them how achieving the team goals helps the members achieve their own goals.  They can learn new things about their field, gain experience performing particular aspects of the job, meet people who can offer other advantages.  Appeal to your team members' personal and professional goals.

I know thousands of books have been written on these topics.  I hope this brief discussion motivates a PM or two to learn more in areas that might be hindering their projects.  I also hope other (non-PM) business professionals gain a little insight into the challenges of project management.