First time clubbing with friends and with a girl I like... What should I expect?

I think you will be dressed fine. Generally, the clubbing scene is slightly dressier than casual. Also, be prepared not to be able to hear anything anyone says. You'll be continually saying "What?" all night. It's so much easier for guys to dance than girls. Take the girl you like on the dance floor and just grab her hips and sway to the beat. Girls like to show off their dancing skills. We don't really expect guys to know how to dance as well as we do.