a rule of thumb:
turn your pole upside down, hold it right under the basket; if your underarm is horizontal and makes a 90°angle with your upperarm you have a good length...
Now a bit more specific: everyone prefers differents lengths; there isn't even a relation between your skistyle; i know ppl skiing pow with short poles and i know people skiing park with short poles and same goes for long poles...
if its your first pair; i advice you to get em like i described above (maybe even a bit longer, you can always shorten your poles but can't stretch em back...)