to start- you should browse through some catalogs and magazines to find about ten different poses. put on some music and get in front of a full length mirror and mimic the poses you found. alternate your facial expressions. then mix and match facial expressions with the different poses you found. before long you should have at least 10-20 poses memorized so you can fall back on them during your first shooting.
you do not need any fancy classes just practice, practice, practice!
you do not want to get on set at a job and not know what you are doing!
what every model needs to know is how to pose, and everybody 