One of the most important parts of a poach is the act of moving forward. Many players try to poach, but in doing so, they move parallel to the net.
When you are in the ready position at the net, most people have close to 180 degree vision. If you use all of this 180 degrees you will often times find yourself moving sideways or parallel to the net. Have you ever seen how horses have "blinders" on during races? This is to restrict the animalŐs vision making it more "tunnel vision" and to avoid to many distractions. In your imagination, place these blinders on yourself. Immediately, you will narrow your 180 degrees vision to 100 degrees of vision. This will narrow your choices, giving you more opportunities to see and move forward.
For example, when the ball is hit to your forehand, for a right hander, and you can contact the ball before it crosses your "blinder-line" (50 degrees off your center to your right), this will force you to move forward, greatly increasing your chances to win the point. If you start too late or fail to move forward before the ball crosses your 50 degrees of vision off of your center, then do not poach.
You will also see how this helps when a ball goes down the middle while you and your partner are at the net. Many players are actually afraid they are going to physically hit their own partner as they both move towards the ball. If both players abide by the rules, they will seldom feel threatened. Thus both players will be moving forward and not parallel to the net.
When you adhere to this tip, your partner will love you.
Good luck on the courts!