I have heard this so many times from recreational players...."I was at the net, ready to poach, saw the ball coming but didn't get there on time" or "My opponent keeps poaching before me and I keep getting hit". The reason this happens is because you are probably standing in the wrong spot to start your poach, are in the wrong spot when your opponent decides to poach and move towards the poach in the wrong direction. You need to understand the optimal movement pattern at the net in the 1 Up / 1 Back Formation. This video will teach you how to move at the net so you can become an effective poacher.
For more video like this, (or to learn Gigi's 2 rules for coming in to the net which she references in the video) consider buying The Gigi Method doubles instructional program.