I asked at hotel reception where the best place to go on a Tuesday night in Vancouver is. I was recommended either Gastown or Granville. Gastown is pleasant enough but was pretty quiet to say the least. I then tried Granville and that was much livelier, not too bad for a Tuesday night at all. I can imagine it gets fairly mental there at weekends.
On a Tuesday night I was recommended by a couple of people to go to a bar called 2 Parrots as the likeliest place to have a bit of a crowd in due to their karaoke night. This proved the case. up to you if can bear the tuneless and the tone deaf who far out weigh those able to select a song in a key they can sing a little bit in.
Granville Street is the place to be in the night time if you want to go dancing, have a drink with friends, or just people watch.
There are so many places to choose from the possibilities are endless....you can dance up a storm, kick back with food, have a loud noisy beer, or a quiet cocktail, or just grab a slice of 99 cent pizza and watch the world go by.
Since there's so many places, it's hard to give a recommendation of where to go on this street...it depends what you like. Some of the more popular spots for dancing are the Caprice and the Roxy. Doolins is a great pub, while you can get cheap eats virtually anywhere.
However, beware of the line-ups. Sometimes you will will wait for hours for a place that is not worth it. Go with this in mind and you should be ok.
Dress Code: Clubs generally require you to look niceish...but again, depends on the club and the day.
The rest of the place is up to you.
If you want to go out where the people are, go to Granville Street. This is as close as Vancouver gets to having a "club district". Most of the city's most popular nightclubs are on this street, as well as smaller, calmer bistros and lounges.