In addition to feedback from people, it's really useful to take video (which is easy these days) and carefully watch it. It really makes you aware of distracting habits and verbal tics.

I have an interview style podcast and editing makes me very aware of verbal tics in both myself and others.

You may find it easier to record yourself while speaking to others though. At least for me, just talking into a camera in my office can feel very awkward.

ADDED: I have taken courses through my employer a couple of times. They've been useful but I agree with everyone else that observing others who you think do a good job, practice, and feedback are generally more useful than taking a course as such. I wouldn't dissuade someone from taking a course but don't go in expecting to learn the magic formula.