Start off throwing dummies randomly whilst you're out and getting the dog to sit, might be more difficult to transfer this to live quarry. Some people make their dogs sit whenever any quarry gets up in front of them. So, you'd just be taking a normal walk, a pigeon hears your dog approach so flies off - you blow the stop whistle and make the dog sit as soon as the bird takes off. Of course, you need a solid stop whistle or if the dog is on the lead you can control it better.
Once you've got the sit to the whistle 100%, then is the time you move onto live game and blow that whistle as soon as anything gets up. It soon becomes second nature to them. Helen