There was not much in the way of nightlife that we came across where we were staying, I am not sure about the bigger towns of Panaji, Margao or Mapusa. There are Restaurants that have live music and some have a sort of sound system that play up to date music but when we were there it did't tend to go on to the early hours. There was a sort of rave scene but it was mostly on the beach with ghetto blasters and on the odd occasional generaters to power the drum and bass. We were quite happy to go back to our hotel balcony with some local produce and a beer and listen to the owls hooting and the other wonderful noises that only the warm Goan nights can produce.
Goa has a vibrant night life. Of course it depends also on when you are there. The 'season' begins in October, after the monsoons, and continues till the Carnival in February. then the crowds begin to thin, as its too hot but there are great bargains to be had!
there are a lot of clubs, the oldest and still the most popular is Tito's on Bagha beach. there is avalon at Colva and the five stars have thier clubs too. shacks stay open till late, serving drinks as well as food! The hotel you stay in will have events planned, so check with them.
Dress Code: dress code isn't strict. the western tourists wear whatever the hell they want. the smaller / shorter the better. some are in tatters - its really sad!
But i would recommend clean presentable clothes - size doesn't matter. Besides, it is so hot and especially with all the dancing, airy cotton , short clothes are really the best!
this is my husband at the resort's valentine day's party! :)