If possible, avoid using taxis and take trams or walk instead. Due to deregulation, a large percentage of the taxi drivers genuinely don't know where they're going. This can work out a bit pricey for a tourist as there's a fair chance you won't know either.
The best bar in Amsterdam is the Bastille Bar near the Leidseplein, which is very popular with the locals. The downside of this is that when they're busy they take the 'members only' attitude and the doormen will turn tourists away.
It's not a bad idea to tip doormen on the way in to a club. The Dutch tend to tip doormen when they're leaving but foreigners don't, so if you want to get onside with these guys offer a few euros on the way in.
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