Obviously, your warm up is the first exercise of class. Whether you're playing for free work classes or for daily company classes - it is my belief that you should choose your warm up repertoire extremely carefully - depending on the standard of dancers you are playing for. Of course - your choice should always be inspiring!!
I tend to favour jazz standards (such as the free PDF download below) especally for company class or for higher dance conservatoire level as I feel and have been told by many dancers that they feel the music 'eases' them into their day. The natural flow of standards and the way you play them can be the perfect start to the class. Obviously many melodies that are 'standards' continue to work increidbly well if you're changing the rhythms slightly (or even time signature eg. 4/4 to 3/4) to reflect a port de bra for example, whilst staying true to the composers intentions.