(Definition: going for a ball in doubles that your partner would hit, but you think you can win the point)
Many times a student will come to see me and ask if I can help with poaching in doubles. It is very difficult to design a drill specifically for poaching. If it does happen, the results in the drill will usually make little improvement in a real match. Why?
Because when you play singles or come from a singles background, you move to every ball without hesitation. If you do not have the background, usually you will hesitate to hit many balls because you think your partner might hit a better shot or you might make an error going for the balls. As a result, this hesitation stops many potential poaches!
How do you begin to fix this (hesitation) problem? When you are at the net, start thinking you are going to poach every ball. Quit waiting for the "perfect ball" to poach. Start committing your racket preparation every time your opponents hit the ball, even if you do not think you can hit the ball. To poach you have to commit your position early on. Remember, poaching is not just hitting the ball that your partner could hit, it's winning the point with the ball your partner could hit. Start committing early and often. Poaching is one of the most fun aspects of playing doubles.
Good luck on the courts!