In early spring you will want to cut back your hop plant shoots but you will only want to cut back the correct ones.  There are two types of shoots that will emerge from the hop plant.  The first ones that come out are called "bull" shoots.  These early shoots will be only a handfull, 3-5 per plant and they will have a hollow stem.  You will want to scout the yard early to see when the shoots come out.  Once you see some shoots emerging from the hill you will want to remove the dirt from the hill and locate the level of the 2nd set of shoots.  They will be separated by inches if not more and the goal is to cut the hill between the two levels of shoots.  By removing the early "Bull" shoots you are also removing any downey that may have attached to the plant during the winter.  You will want to BE CAREFUL not to cut below the 2nd level of shoots, this will affect you'r yield.  We recommend you remove the soil in one hill in ONE varieity, measuring the difference and then cutting above the 2nd level.  Once you do one plant and identify the location where to cut, you can cut the rest with an automated tool such as a mower or weed eater.  VERY IMPORTANT:  This will be varieity specific so make sure you look and work per varieity becouse each one may be different and you will NOT want to cut the 2nd level of shoots by mistake.

Information Below is from Professional Hop Grower Lynn Kemme:

The first largest bines to emerge on 2nd year or older hop crowns are not necessarily the best to train. These "bull" shoots have a large hollow core, like a straw; and easily kink or are damaged by late spring storms. Most crowns put out two to three of these, at the most; and crews can be trained to identify them and prune them out as they twirl climbing bines. "Bull" shoots are often a light olive green color with stretched internodes - some field practice clipping a few will reveal which have the hollow stems.  

More Info. By Steve Schmidt

Using the "Bull" Shoots will lower your harvest yield due to the stretched internodes.  With stretched internodes you will get less side arms, by using the 2nd shoots that come out you will have less internode spacing and that in turn increases the number of side arms and increases your harvest yield.