During the Summer, it's common for Ecuadorians from around the country to vacation in Montanita.
99% of the time you won't need to worry about dressing up for a night of partying in Ecuador.
Nightlife in Ecuador is pretty quiet Sunday through Wednesday unless you know the right places to go to (hint: ask the locals).
Otherwise, look for flyers advertising ladies nights early in the week.
Most of the bars and discotecas in the pueblos, such as Banos and Montanita, are centrally located.
Just follow the music, and you should have no trouble finding the action.