it really depends on the club.
Sugar, Hei Hei, Dragon-i are pretty strict on dress code/who gets in. Nobody is mean, but they will turn you away if 1) they are full or 2) there are other "members" that are waiting to get in.
Most of the other places are easy to get into unless you aren't dressed nicely. Just no shorts, no flip-flops or collar-less/sleeveless shirts for the guys. Pretty much anything but flip-flops go for the girls.
Also, flirting with the bouncers (if you are a girl, or a guy with a lot of girls, or a guy with a really hot girl) usually will get you in too
c