Here's what I've gleaned from other threads on the topic and my own (still limited) experience:

:: The most essential thing to avoid is mentioning anything about rates and/or services in your communication with ASPs.  
:: For telephone calls/messages make sure the number from which you are calling is not blocked.  Many ASPs will not answer calls from or respond to voice mails from blocked numbers.  You can unblock and individual call by preceding it with *82.  
:: Review the contact information section of the ASP's web site or ad.  Some have preferences for how they like to be contacted, and for some this is especially true for first-time contacts.  
:: For the sake of discretion, if more than a certain small amount of time (say 10 minutes) has passed since you left your message an ASP will not call you back unless you explicitly tell them it is okay to do so in your message.  This is to avoid creating potential embarrassing or uncomfortable circumstances for you.  
:: The more specific you can be in your message (within previously mentioned limitations) the better and the more likely a busy ASP will be to return your email or call.  For example, specify the timeframe for which you'd like to make an appointment and if the ASP offers both in-call and outcall services specify which of those you are seeking.  
:: If you have references mention them in your message.  If you don't state that as well (you'll get points for being forthright).  
:: Do your homework.  Don't ask questions that are answered on the ASP's web site or by the ASPs readily available ads.  
:: Mention where you found about about the ASP.  It helps to affirm that you've done your homework.  
:: If you are a newbie, state it up front.  It will become clear anyway and by admitting it you will be going a long way to establishing a better relationship.  It can help the ASP be a little more tolerant of your foibles as well.  
:: A debatable point is to tell the ASP a little about yourself.  Avoid being too wordy though.  You don't want to come across as being too high-maintenance.  
:: It probably goes without saying, but if you are rude, crude and disrepectful, don't expect to get a reply.  
:: Don't always assume that a lack of reply from a particular ASP is a deliberate shun.  Sometimes they have technical difficulties with their voice mail and/or email.  If one medium doesn't work try the other.  On the other hand don't be a pest either.    
:: If you don't hear back from them, they may be out of town.  Try back some other time.  
:: Has anybody ever told you that your voice sounds creepy (e.g., like Jack Nicholson's)?  If so, you might not want to use the phone.  

Thank you all for your help. I have been very nervous about making first contact as I expect a lot of newbies are. I want to put my best foot forward and increase the chances that this particular provider will accept me as a client. After much research, I think she is the one who will provide what I am looking for. Thanks again!