if you're willing to spend some money, then best bet would be to
be generous and buy drinks for that girl you eyed and her
friends.
well in my opinion, best method is to catch her eyes firs. make
sure you and your friends seem to be having a great time. let her
notice you. then you look back at her and smile...If she smiles
back, then approach for the small talk and perhaps buy a
drink.
On the dance floor its gonna be pretty hard. she'll probably think
you're a pervert who wanna molest her. haha so just act cool on the
dance floor and groove. if she takes to your fancy, she will dance
with you.
Just smile and have a great time!hope this helps