Preventing the Guard pass is the most important aspect of Jiu-Jitsu. The position is called Guard for the very purpose that the Guard position is what protect the bottom fighter from being attacked. Loose the Guard and you will not only be vulnerable to attacks but you will also start to get tired, once tired your technique will start to suffer.
Be sure to train your Guard preventions above all. Having a difficult Guard to pass will allow you to relax and have the confidence to attack you opponent. The harder you Guard is to pass the more you can open up and take chance.
Be sure to work this sequence it is a very power recipe for Guard retention.