This newbie needs help! (Or possibly just a backbone...)

First of all, I just want to say thank you, thank you, thank you, to all of you for your wonderful posts, and sharing your insights and experience.  I am brand new to this business, and finding AR has only increased by excitement!

There is one area, however, that does not exactly... excite me.  The actual "business transaction" part of working with a client.  I find it so awkward to bring up the subject of "now here's the part where you pay me..."  HELP!  Will you please share how you go about doing it?  I would be so grateful!