Some say that brushing the sole is important. I am fortunate with the studio I dance: the floor is very good and so I brush my shoes like in every 3 month.
Competitors frequently use water, but I do not recommend that it is bad for the sole and the effect lasts for 30 seconds or so.
What worked for me on slippery floor is to concentrate on the inside edge of my ball of feet. Putting more weight there helped me with balance on slippery floors.
And finally I had the chance to ask Luca Baricchi about this!! He said that a kind of medical substance or oil can be applied to the soles if it is really bad, if I remember correctly it was something used against bad stomach... Unfortunately I had no pen with me to take a note.
Matyas