There are two schools of thought regarding the pull-up - Strict or Kipping. The Strict Pull-Up (SPU) is the standard for many (including the RKC community) and the Kipping Pull-Up (KPU) is pretty much the standard in the CrossFit community.
There has been a lot of debate as to which is better or worse, which has more application in real life, etc. As far as I'm concerned they are both valuable tools and need to be developed - eventually. In class we emphasize the KPU to get people moving fast over the bar and to keep the intensity as high as possible. When I want to slow things down and focus on tension and technique I like to emphasize the SPU. I try to equate the two as one being a Grind (the SPU) and one being a Ballistic (The KPU). You need to have both but not at the same time.
For a good tutorial on the KPU take a look at this video from SurfBody Fitness:
BTW - if you don't have a Pull-Up at all then you to get one... through hook or crook! There are a lot of accommodations (bands, boxes, pulleys, etc.) to get you over the bar, but eventually you are going to need to do it on your own - start now!