When I use my machine I typically start with a cone drill where I put an orange cone about 6 feet away from where I'm hitting and shuffle around it between each shot to help with footwork.
To help with doubles I will line up so that the balls are being throw directly at my right hip in order to practice awkward volleys. Or alternatively I'll crank up the ball speed and stand where the balls are being shot at center mass to work on reflex volleys. I have found it hard to get other players to work with me on volley drills at all, much less getting them to pound them straight at my body consistently.
Another thing that has helped me in doubles is to work on half-volleying by setting the machine so that shots are hitting right about the service line where my feet would be if I was coming in after a serve. I then practice coming in a few steps, split-stepping, and hitting a shoe-string volley or half volley. Being able to hit a few hundred of these in a row has improved my net rushing success by quite a bit.
Putting your machine up on a cart or even getting it higher than that to throw balls helps better simulate serves so you can work on returns of serve. I've posted a video of how I set up my machine to do this, as have other posters, but I don't do it much because it requires too much set up time.
When should you serve and volley in doubles? Only when you want to win.
Last edited by beernutz; 12-03-2012 at 08:53 AM.