The first call is when you call the agency once you arrive at the providers location.  The agency then calls the provider to let her know you have arrived and ask her if she is ready for you.  The second call is when the agency calls you back to let you know the provider is ready and tell you her room/apartment number.

With an independent lady, 2 call works a bit different.  She will call you once with the general location.  (I am at hotel XYZ, at nth street and main) and she will call you again right before your date time with the room number.  In some cases, I have had ladies ask me to call them to get the general and specific details.  So be sure you understand who is to initiate the calls.

Re prep for the meeting. Approach as if you were getting ready for a date with a hottie you have had a crush on and now she agreed to go out with you. Expect to have fun, and you do not need to worry about "getting lucky". Best advice is to just relax. Do not build up too many expectations.  Once the date starts, things will move along at their own pace.  I have found that it is best to let the lady take the lead, since I am relatively new myself.  Good providers know how to set the pace. They want to get to know you a bit in first time meetings, but will manage the time so that you are satisfied when you leave.

Preparation or "practice" by oneself before seeing a lady would depend on age.  I'm past 50 so I abstain for a week or so in order to be able to attempt MSOG.  If I was in my 20's again, I do at least one "by self" to prolong the first with the lady.