Well first you have to make sure you have attraction, in a night club setting I generally hold her hand and lead her to the smoking area or something. Once shes attracted to you and is comfortable enough to know you're not going to chop her up into little pieces you can get to work.
You do not have to make your intentions know verbally, instead you can be physical. For example if im holding her hand and im facing her, I put my other hand on the small of her back and hold her in a little closer, maintaining eye contact. If shes not into you, she will let you know then because thats pretty suggestive. If she is, you can get closer and closer until you kiss.
A number is not a big deal, she might not even reply, instead see a number as a way to continue on your conversation. So if you've had a nice chat etc just be like "hey ive got to run but it would be nice to continue this later, lets exchange numbers" or something like that.
