Smoke lots of weed, go to Anne Frank's house, go to the Van Gough gallery (and the Rembrandt gallery the second time you go). The canal breeze makes their winters seem colder and harsher than the UK, but it's still worth a trip even at that time, just wrap up warm.
Most places won't allow you to drink AND smoke weed, but there is one former coffee shop-turned-bar where you can go downstairs and do this. I can't remember the name though. Also there's places that do bongs that are basically like breathing in air from a balloon, but again I can't remember the name of the place. As you can tell, there's a running theme here, but there's a reason for me not remembering much as it's all a haze
Punting wise? It's not actually that good. Not sure about what it's like for gays, but for straight guys there's plenty of choice, and no chance of a bait and switch, so you feel like a kid in a candy store walking around the streets admiring the sights in a thick crowd of staring tourists. But everything is dimly lit, at least 50 tourists will see you on the way in and way out (opposite of discreet), the girls rush you and you may not be in a stable enough state to perform anyway if you're doing the rest of what Amsterdam offers
Finally, a guide I read somewhere else on crossing the street in Amsterdam:
look left
look right
look left
look right
look up
look down
look left one more time
look into the 4th, 5th and 6th dimensions
look into the past and the future
look into the souls of your unborn children
cross
still get hit by a bike
