Fly to Östersund through Stockholm.
the flight from stockholm is about 45 minutes. you can get on a bus to Åre from the airport, or pre order a shuttle for like 300 SEK (50 bucks).
your other option is to fly to Stockholm, get on a train to the Central Train Station (20 minutes), and from there get on a train to that takes you straight to Åre. it takes about 8 hours but if you get an overnight train you can get a bed and just sleep through it. The train is like a hundred bucks.
I'd take the train for sure, then you might get a few hours in downtown stockholm too.
Getting a place to stay in Åre isnt easy and it will cost you a lot. If youre on a budget, try to get a room or a condo in either Björnen or Duved (both are about 5 minutes on the bus from the village). it will be a little more expensive for you to get home after partying, but you can always team up with someone and catch a cab back (about 40 bucks).
The bus is free if you have a lift ticket.
pm me if there is more you need to know.