There are 3 paraliminals that come to mind that would help you in your situation.
Relationship, Instantaeous Personal Magnetism and one oft overlooked Sales Leap
Personally I think Sales Leap would be your best bet, since you summed up in your post the desire to improve verbal communication. It isn't really about becoming a Sales Man but more having confidence when communication with people so that you can positively interact with them. It's a skill that successful sales people have. Being able to communicate with others easily.
Sales Leap is good one if you have to do public speaking, standing up before a group for presentations and if you know you're going to be in a gathering of people.
Use it the day before if you can or night before.
The other 2 would also help with how you relate to others also.