The way I always do it is to 'dog in' for the local shoots. Especially before the season starts. If you have a word with the keeper he/she may let you dog in the boundarys of the shoot.
have you trained your dog to 'sit/stop to flush'? If so, the second it flushes a bird get on that stop whistle as fast as you can. I always keep my whistle in my mouth at all times when working my dogs, it saves vital seconds in fiddling around!!
Also, like alot of guys on here have said, a few days in a rabbit pen which hopefully should have some birds in there too will certainly help! Then I would move